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Open Water Swimming

Medical and Water Quality Considerations

Chamberlain, Matthew, MD1,2; Marshall, Ashley N., ATC3,4; Keeler, Steven, MD5,6,7

Current Sports Medicine Reports: April 2019 - Volume 18 - Issue 4 - p 121–128
doi: 10.1249/JSR.0000000000000582
Environmental Conditions/Section Article

The sport of open water swimming (OWS) has been popularized on a global scale. This population of athletes may experience several unique medical conditions, necessitating a review of medical issues and environmental considerations. Clinicians providing care for OWS athletes should be educated and trained to recognize and manage illnesses and conditions that often occur in an effort to ensure athlete safety. This article focuses on the major medical challenges faced in OWS, including a review of cardiorespiratory conditions and infections, competitor factors, water quality concerns, and risk minimization strategies.

1The Melbourne Sports Medicine Centre, Melbourne, VIC, AUSTRALIA;

2Swimming Australia, Brisbane, AUSTRALIA;

3Department of Interdisciplinary Health Sciences, A.T. Still University, Mesa, AZ;

4Sports Medicine and Science Network, USA Swimming, Colorado Springs, CO;

5Department of Family Practice, University of British Columbia, Vancouver, BC, CANADA; and

6Canadian Academy of Sports Medicine, Ottawa, CANADA;

7Swimming Natation Canada, Ottawa, CANADA

Address for correspondence: Matthew Chamberlain, MD, Melbourne Sports Medicine Centre 4/250 Collins St Melbourne AUSTRALIA; E-mail:

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Open water swimming (OWS) events are becoming increasingly popular around the world. Any event held outside a swimming pool constitutes an open water event (1), and they may be held in rivers, lakes, oceans, and seas with exposure to challenging environmental conditions and pollution. Some of these unique environmental challenges have been brought to public attention in the lead up to both the 2016 Rio Olympic Games (2) and forthcoming 2020 Tokyo Olympic Games (3). OWS medicine is relevant to OWS, triathlon, as well as surf lifesaving. OWS as a discipline itself has been sanctioned by the Federation Internationale de Natation (FINA), the international governing body for aquatic sports, since 1986 (4). The sport has been a part of the Olympic schedule since 2008 as 10 km marathon swimming, and events have been incorporated into the biennial FINA World Championships since 1991, at distances of 5 km, 10 km, and 25 km.

Sports medicine practitioners need to be aware of the medical issues unique to swimming in the open water, understand the risk of exposure and potential consequences to athletes. This review will outline the major medical challenges unique to OWS, the risk of which can be moderated by optimal event planning, race day strategy for dealing with medical issues, and knowledge of current risk minimization strategies. This review will not cover musculoskeletal issues, as the issues are very similar to pool-based athletes and reviews of this have been covered previously (5).

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Medical Issues in OWS: Cardiorespiratory

Effects of cold-water immersion

Before discussing cardiorespiratory issues in OWS, it is worthwhile to consider the stages cold-water immersion (CWI), their physiological associations, and risks. The four stages of CWI have been defined as (6):

  1. Initial immersion (0 to 3 min) — the initial period is associated with highest risk of fatal outcome (7). Skin cooling occurs and can trigger a “cold shock” response.
  2. Short-term immersion (3 to 30 min) — the short-term period is associated with neuromuscular cooling.
  3. Long-term immersion (30 min plus) — the point at which deep core temperature may drop, and hypothermia ensues.
  4. Circumrescue collapse — occurring around the time of rescue, athletes may be subject to increased risk due to behavioral or rapid reversal of physiological changes. After-drop phenomena also may be seen.

Cold shock is an athlete’s initial response to CWI (8), and occurs within 30 to 120 s of exposure. It is noted in water up to 25°C and increases until water temperatures of 10°C to 15°C (9). Athletes may experience a gasp response, hyperventilation, heart rate elevation, and possibly loss of consciousness. More significantly, drownings and myocardial infarctions also are potential consequences (10) (Table 1).

Table 1

Table 1

Neuromuscular cooling seen in short-term immersion, may lead to physical incapacitation (11). Decreasing muscle temperatures affects multiple biochemical and physical functions down to a cellular level. Changes in both muscle function (strength and power) and nerve conduction velocity have been noted, with the potential dysfunction leading to a relative paralysis and subsequent drowning risk (7). The effects of true hypothermia are discussed in a subsequent section.

The circumrescue collapse accounts for 17% of deaths (12). Although incompletely understood, behavioral change has been implicated and has alteration of resting catecholamines and increase vagal tone due to relief from imminent rescue. After-drop refers to the continued fall in core temperature after removal from cold stress (13), and can occur up to 1 h postcold immersion. This condition ensues when cooled blood from the periphery returns to the core post exercise and can be worsened if warmed core blood is shunted to the periphery. In addition, after-drop can occur in triathlon when vigorous biking exercise occurs post cold-water swimming and smaller individuals are likely at more risk (13).

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Sudden cardiac death

Most swimming-related sudden cardiac death (SCD) occurs during open water competition, but rarely in training. In the 2012 US Triathlon Fatality Incident study, of the 43 triathlon related deaths, 79% occurred during the swim (14). Additionally, a recent case series (15) evaluated SCD in US Triathlon participants between 1985 and 2016 and had similar findings, with two thirds of the 135 total deaths occurring while the participant was swimming. Cardiac abnormalities are well recognized in endurance athletes. Cardiac issues such as undiagnosed coronary artery disease, hypertrophic cardiomyopathy, arrhythmias, Wolff–Parkinson–White syndrome, and long-QT syndrome, can be causative factors (16). Autopsies on open water triathletes who have died in swimming competitions confirm the presence of cardiac abnormalities (17). Current literature (18) proposes that the occurrence of “autonomic conflict” (AC), which is the coactivation of both divisions of the autonomic nervous system, can lead to SCD, particularly in open water competition. The sympathetic nervous system is activated by cold shock (i.e., the autonomic response to a rapid submersion into cold water) (18), anger and anxiety (19), whereas the parasympathetic nervous system is activated by breath holding, facial wetting, and water in the nasopharyngeal region (5). This conflict can lead to fatal cardiac arrhythmia, usually ventricular fibrillation (18,20). The originators of this theory astutely point out that sudden death incidents reported in OWS occur almost exclusively during competition events and not in open water training or swimming pools (9), this lending further support to the concept of AC as a causative factor. This remains an intriguing and plausible theory to explain sudden death in OWS competition. There unfortunately remains very little evidence to support alternative causes, such as swimming-induced pulmonary edema (SIPE), exercise-induced bronchoconstriction (EIB), extreme water temperatures, and so on (Table 2).

Table 2

Table 2

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EIB is a common problem in aquatic athletes, and has been reported to occur in up to 50% of swimmers (21). While the condition is frequently diagnosed in pool swimmers (21), OWS athletes will typically complete some of their training in the pool environment, thus increasing their risk. In addition, swimming in cold environments also is a significant risk factor for EIB (5). Awareness of common symptoms, such as wheezing, chest tightness, cough, and shortness of breath within several minutes of high exercise intensity, can aid in diagnosis and management. Medical staff covering open water events should be aware that anxiety with panic attack, vocal cord dysfunction, and cardiac arrhythmia can mimic EIB. It should be recognized that many swimmers will not have symptoms at rest. Practitioners should have a high index of suspicion for this condition, particularly in those athletes with atopy, family history of asthma, quick onset fatigue during exercise, rhinitis, etc. Suspected athletes should be screened with initial basic spirometry and if negative, consider provocative testing such as methacholine challenge, sport specific exercise challenge or eucapnic voluntary hyperpnoea testing.

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OWS can present considerable risk for the development of hypothermia-related illness in athletes (8,10). Hypothermia occurs in the context of net heat loss, and in OWS is largely related to the greater thermal conductivity of water and permitting cooling at a three to five times faster rate, meaning hypothermia may have more rapid onset in OWS athletes. Any temperature regulatory disorder is based on assessment of the deep core temperature (22), and all OWS medical teams should be aware in particular that aural tympanic membrane measurement is not an accurate measure in cases of CWI (23). Mild hypothermia is defined as a core temperature between 32°C and 35°C, with evidence of shivering, elevated heart rate and respiratory rate, as well as excessive clumsiness or excitement (22). Moderately hypothermic athletes will have a core temperature between 28°C and 32°C, reduced heart and respiratory rates and may present as confused and exhausted (22). Severe hypothermia is defined as a core temperature of less than 28°C, with rigidity, bradyarrhythmia, loss of consciousness, and loss of reflexes (22). Although each stage represents a progression of cardiorespiratory, cognitive, and muscular function, it should be noted that there is a degree of cognitive dysfunction at a core temperature less than 34°C (24). The most vulnerable athletes are those with poor fitness, the least subcutaneous fat, and the largest surface area (8).

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Exercise induced hyperthermia is a leading cause of mortality in endurance sport (25). Heat stroke is defined as a core temperature greater than 40°C and can be deadly if it goes unnoticed. It occurs when heat production exceeds the body’s ability to dissipate heat to the environment. OWS athletes lose the ability to regulate their body temperature, as sweat evaporation is not possible in the water. Both convection and conduction are greater in the water compared with land sport, often leading to heat gain during the swim. If the water temperature exceeds the athlete’s skin temperature, heat gain will occur creating an elevation in body temperature. Radiant heat gain via the sun is often a factor in these events (26), as OWS suits are often black neoprene and absorb a considerable amount of heat. If a race is to take place in a hot, sunny environment, health care providers and race organizers should make every effort to provide shaded holding areas for athletes leading up to the race start. Clinicians should be aware that performance and safety are affected by increasing water and solar temperatures, intensity, and immersion time (27). In addition, clinicians should be aware of overheating at the race finish and assist swimmers with cooling via suit removal or rapid cooling (i.e., ice bath) (28). Heat acclimatization may be of benefit to some athletes, as it may allow athletes to increase their work capacity in hot environments and reduce exertional heat illness risk. However, it has been shown to be an ineffective and nonergogenic strategy for swimmers (29).

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SIPE has been popularized as a likely cause of SCD, however this link has not been supported by previous studies (14). SIPE is a condition that may present with dyspnea, cough, pink frothy sputum, and occasionally chest pain either during or shortly after swimming (30). Objective findings include pulmonary edema on chest X-ray, O2 desaturation, and inspiratory crackles. An echocardiogram is typically normal, and spirometry may show a restrictive pattern. The incidence of SIPE is poorly defined. In a self-reported case-controlled survey of 1400 triathletes (31), 1.4% reported symptoms suggestive of SIPE. Swimmers presenting with SIPE are often healthy but tend to be older, female with comorbidities of hypertension, left ventricular hypertrophy, and valvular disease (31–33).

Hyperhydration, longer event distances and cold water also have been implicated (34) as potential risk factors for this condition. Additionally, a past episode of SIPE raises an athlete’s risk for recurrence (35). SIPE is thought to occur following immersion, as this can cause central blood pooling from peripheral vasoconstriction and redistribution and increases cardiac preload and pulmonary artery pressure. In addition, there is an increased hydrostatic pressure gradient from a head/thorax body position. These conditions result in increased pulmonary capillary pressure and eventual pulmonary edema. SIPE is treated with oxygen and diuretics, with most cases resolving within 24 h to 48 h.

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Medical Issues in OWS: Infection

Gastrointestinal infection

There has been evidence since the 1950s of an association between recreational water use and risk of gastrointestinal illness. A recent meta-analysis (36) indicated an increased risk of any illness (odds ratio, 1.86) from bathers compared to nonbathers. A variety of gastrointestinal illnesses have been reported from bacterial, viral through to protozoal infections. For the users of coastal water and rivers the most likely pathogen is viral (37). Gastrointestinal illness due to recreational water exposure is usually mild, and many cases may go unreported (38). There is particular concern for the elite athlete given the purported potential immunosuppression in highly trained athletes (39), that they may suffer more severe or prolonged consequences.

Several studies have investigated the risk of infection following OWS events, particularly in the sport of triathlon (40,41). In addition, case reports that have documented significant increased risk of illness due to exposure to water bodies, particularly those with sewerage overflow or flash flooding, have been associated with outbreaks of gastrointestinal disease (42,43). Parkalli et al. (42) observed an increase in incidence of gastrointestinal illness from 8% in 2010 to 42% in 2011 (RR 5.0), explained by racing shortly after extreme rainfall. A similar scale increase in risk was seen after urban canal swimming events in the Netherlands, following heavy rainfall (44).

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Ear infections

An association between open water exposure and ear infection has been noted in previous studies (45). The relationship is not as strong as those documented for gastrointestinal illness and was associated with higher fecal indicator loads. Additionally, a cluster of otitis externa caused by Pseudomonas aeruginosa was reported in association with swimming in fresh water with normal fecal indicators in extremely hot weather (46).

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Dermatologic conditions

In many circumstances open water swimmers are exposed to significant amounts of UV light and are at risk of sun-related conditions including basal cell carcinoma and melanoma (47). Thus, the use of broad-spectrum sun screen protection is strongly encouraged in OWS. A pruritic dermatitis known as “Seabather’s eruption” also is seen in warmer waters after swimming, most commonly related to saltwater species of jellyfish that discharge a nemocyte (48). This contains an antigenic toxin which can be trapped under a bather’s suit (48).

Cold urticaria is a skin reaction often seen in OWS (47), and generally develops within minutes of cold-water exposure. It is most common in young adults, and with a slight female preponderance and average duration of symptoms 1 h. Minor reactions often include red and itchy hives; however, individuals also could experience more severe reactions such as anaphylaxis or angioedema (49). By its nature, severe reactions are often a consequence of the full body exposure to cold water. First-line management is with second generation anti-histamines at up to four times standard dosing, but the most effective management tool is avoidance of exposure (49).

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Medical Issues in OWS: Human Factors

Several human factors can influence the safety of OWS athletes. In particular, participant demographics and nutrition may affect performance and ultimately athlete safety (50). Elite open water swimmers are shorter and lighter than competitive pool swimmers (51), which may be beneficial to their performance. However, as previously stated, a lower body fat percentage also puts these athletes at risk for hypothermia (51). Additionally, these swimmers often compete at or near their anaerobic threshold during competition (51). Consequently, an athlete who is not able to sustain this performance level during training may require additional monitoring during the race. In elite international competitions, the top 10 male finishers were between 24 and 28 years of age and females between 22 and 24 years of age, dependent on the race distance (52). Opposite of pool swimmers, where peak age increases with decreasing race distance, peak age increases with increasing race distance in open water swimmers (50,52). Thus, younger and less experienced athletes require further surveillance during competition. Adequate ingestion of a carbohydrate solution during a race (i.e., “feeding”) prevents hypoglycemia, supports carbohydrate oxidation, and improves endurance capacity (53). It is important to note that very few studies regarding nutrition have been conducted on open water swimmers, and a majority of the recommendations stem from other endurance sports with similar physiological requirements (50,54).

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Water Quality Issues in OWS

Water quality standards are present worldwide, through the World Health Organization (WHO) (37) as well as through many national bodies (55), with the goal of ensuring safe recreational water use. These guidelines help identify important quality issues pertinent to OWS. The Australian National Health and Medical Research Council (NHMRC) guidelines (56) identify seven major facets for assessment of recreational water including natural hazards, environmental hazards, microbial quality, cyanobacterial quality, hazardous wildlife, chemical quality, and aesthetic quality. Understanding these components lends a good base to establishing open water course safety. Additionally, water quality may be altered as a consequence of weather, watercraft, or other human activity. In particular, high rainfall and run-off or churning up of the lake or riverbed can increase bacterial, microbial and chemical water content (41). While athletes may not necessarily experience adverse effects due to these conditions during the race, they may experience gastrointestinal symptoms or illness after competing (41,43,57).

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Natural hazards

Establishing open water course safety will often start with review of any natural hazards (4). This covers natural features of waterways such as beach topography, submerged objects (reefs, coral, and rocks), rips/currents, wave breaks, and water depth. These features will often be known/well-established by regional/local authorities prior to an open water event, mandating close liaison with these authorities to establish a safe course for open water racing.

The presence of rips and currents are especially important in larger community events with swimmers of all abilities. Often, rips can travel up to 5 km·h−1, and weaker swimmers can become rapidly exhausted swimming against the tide (58). Low lying sandbars are problematic on a course, especially close to shore where the waves break leading to “dumping” of the incoming swimmer. This phenomenon also occurs in rivers and lakes, which are particularly prone at times of high rainfall or tidal inflow/outflow. FINA open water rules (1) mandate a minimum water depth of 1.40 m at all points on the course in an attempt to mediate some of these natural hazards.

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Environmental factors

Ambient air temperature, water temperature, and UV radiation exposure are important considerations in OWS. As previously noted, hypothermia and hyperthermia are major medical considerations in the sport. Current FINA Open Water guidelines (1) mandate a water temperature between 16° and 31°C as measured 40 cm mid-course 2 h before racing. The International Triathlon Union (ITU) guidelines vary slightly, suggesting measurement at three points along the course, at a depth of 60 cm an hour before racing (59). There is variation in minimum temperature across organizations – FINA guidelines suggest a minimum of 16°C, ITU suggests a minimum level of 12°C and British triathlon suggests 11°C (10). In 2017, FINA adjusted the apparel rules for OWS (60): when water is greater than 20°C swimsuits should not cover the neck, extend past the shoulder or extend past the ankle; when water is between 18°C and 20°C swimmers may use either swimsuits or wetsuits; when water is below 18°C the use of wetsuits is compulsory.

In general, there is wide variability in a swimmer’s ability to tolerate water temperature extremes, related to previous exposure and duration of exposure, anthropometric characteristics (i.e., body weight, subcutaneous fat), conditioning and aerobic fitness, and swimming speed. The use of wetsuits allows the athlete to better tolerate the colder water for longer periods, but can theoretically be problematic at warmer temperatures (10). Again, variation in guidelines exists across the world, but wetsuits are discouraged from races less than 1500 m at 22°C, and from races greater than 1500 m at 24°C (10).

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Microbial quality

Observation of recreational water quality indices has been performed for more than 50 years now. While outbreaks of multiple bacterial, viral, and occasionally protozoal pathogens are often reported in open water, it is not pragmatic to test for these all routinely. Most recreational water bodies contain a mixture of fecally derived pathogens and nonpathogenic fecal indicators, derived many sources including from waste water, industrial effluent, rubbish, domestic animals, and wildlife. The standard observational indices are surrogate markers as measured by coliform bacteria and enterococci levels (61), but vary in their usage across recreational water regulatory bodies. A 2003 meta-analysis (57) demonstrated an association between increasing enterococci and Escherichia coli concentrations and gastrointestinal risk.

The ITU guidelines (61) (Table 3) are representative of excellent quality recreational water (EEC guidelines) from both sea and inland water. FINA guidelines (1,4) for OWS are consistent with standards of the governing local recreational water authority. For instance, as the FINA rules cover the 2020 Tokyo Olympic games, fecal coliforms will be assessed, along with other water quality parameters such as presence of oil film, chemical oxygen demand, and water transparency. ITU recommendations (61) note that water quality testing should occur 1 year, 2 months, and 7 d prior to the main event. This testing must be done generally at three points along the course of the swim.

Table 3

Table 3

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Cyanobacterial quality

Cyanobacteria (blue-green algae) are naturally occurring and a part of most water ecosystems. They are not frequently an issue for OWS events but have potential to increase to such volume where they may discolor the water. Cyanobacteria are of concern due to toxin production that may have harmful effects on athlete’s health (62). In low numbers, cyanobacteria pose little risk to the athlete. However, in larger numbers, where surface changes are visible, the bacteria pose a greater risk. Cyanotoxins have been shown to have hepatotoxic, neurotoxic, and most commonly dermal reactions. Currently, there are no studies that have examined the effects of blue-green algae on OWS athletes; however, military personnel have contracted illness following exposure to high levels of cyanobacteria (63) (Table 4).

Table 4

Table 4

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Hazardous wildlife

Avoidance of dangerous animals that are found in several open waters is of utmost importance. These animals are usually region-specific and can interfere with athletes in several ways, and at several points during an OWS event. As the exposure risks are very often region and season specific, it is recommended that early contact is made with regional surf lifesaving association/water quality authorities to better understand risks.

Injuries related to aquatic organisms are sustained in ways such as:

  • Inadvertent contact with a floating organism such as a jellyfish (e.g., Australia Irukandji, box jellyfish). Several species are common in warmer Australian over the summer months and can be associated with anything from minor skin reactions to severe envenomation anaphylactoid reactions.
  • Inadvertent contact with a dangerous organism upon entering or exiting the water (e.g., stonefish, catfish).
  • Swimming in the waters of territorial animals such as sharks, rays, or crocodiles. Although there is concern about these attacks, events during swimming/triathlon are very rare.

Risk is managed primarily through education and awareness of OWS athletes and ensuring that the medical team is aware of the appropriate treatment strategies for accidental envenomation, including rescue and lifesaving methods, removal of tentacles, immersion in vinegar (Only for: Australian Irukandji, Hawaiian Box Jellyfish, Pelagia noctiluca), immersion in hot water (unless Australian box jellyfish), consideration of cold packs for tropical stings, and symptomatic treatment (64).

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Chemical and aesthetic quality

Risks associated with exposure to chemical contaminants are generally small in OWS. The main sources of chemical pollution are from industrial waste and flow off from farms. The WHO (37) suggests that individuals with single or multiple exposures to chemicals are typically unlikely to suffer adverse events.

The aesthetic quality of the water is measured via transparency, odor, and color (61). Water transparency is important to allow swimmers to judge depth of water and avoid submerged hazards. It can be affected by many factors, including algae, minerals, and debris, as well as turbidity, but is poorly understood in the context of sea water. Events held in estuarine waters are often darker due to increased turbidity and may give misconception about pollution. Oily substances may form a film on the surface in only trace amounts; however, the ITU guidelines (61) suggest that oil should not be visible on the surface or detected by odor. Litter is an increasing problem in waters surrounding urban areas and may contain many by-products representing a proxy risk for gastrointestinal symptoms/infection following water exposure (65).

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Decision Making and Legal Issues

The preceding section outlines desired standards for safe OWS racing. At times various challenges such as ocean conditions (e.g., excessively large surf, currents, or rips), water quality issues (e.g., microbial contamination) or environmental extremes (e.g., water temperature) may lead to concerns about athlete safety. At this point a decision must be made about whether to modify, postpone, or cancel the OWS event. This decision process should be made in liaison with the medical director, race director, and event manager, but is generally sanctioned by the race director. Safety of the athlete is always the primary concern in the decision making process. The decision making process is made easier with clear advanced planning, and presence of a clear OWS event contingency plan specific for each potential environmental concern. Important components of forward planning include establishing a clear chain of command for decision making, designated monitoring of weather conditions, and water temperature quality and identification of alternative courses and entry/exit points. These strategies, particularly in the lead-in to the event allow for early notification of athletes of potential changes, and early dissemination of information.

From a medico-legal perspective, medical personnel should be aware that although most OWS events will have event liability insurance that this will not extend to medical liability. Competitors also will sign a waiver that covers the general risks from participation in the event the athlete becomes sick or is injured. However, these waivers while broadly encompassing do not cover all scenarios, and do not extend to gross negligence (66). This is particularly important when deciding whether to hold an event in conditions outside the locally or internationally held standards. Any subsequent illness or injury may leave medical personnel exposed to increased risk of legal claim. Medical personnel working on a voluntary basis at an OWS event also should be aware that they will not in most circumstances be covered by “Good Samaritan” legislation which extends only to emergent care (66).

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Event Management for OWS

When planning an open water event, there are several critical variables that the organizing committee must consider. From a medical standpoint, these range from on-water supervision of swimmers, to medical triage, to emergent medical transportation (67). FINA, published an OWS guide in 2015 (4). While this guide aids in the development of officials within the sport, it also serves as a resource for the organization of FINA sponsored OWS events.

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OWS is an evolving discipline with its own unique set of medical problems and event management issue. As the sport increases in popularity, it is beholden upon the sports medicine professional to be aware of specifics to training and competing in the open water.

The authors declare no conflict of interest and do not have any financial disclosures.

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