Open Water Swimming (OWS)

Open water swimming is coming back, in a big way, and recreational water sports are gaining popularity in cities around the world. Over 3,000 open water swim (OWS) events are held yearly on six continents in all types of water bodies. Further, open water swimmers around the world can compete against each other through the Global Swim Series. Swimmers get points for their ranking in swim events happening across the US, Canada, the UK and Europe.

Distances for OWS events range. During some events swimmers spend long periods of time in the water. For example, the Manhattan Island Marathon Swim in the US is a 28.5 mile (nearly 46 km), where swimmers spend over 10 hours in the open water. In addition to open water swimming, there are thousands of triathlon type events that take place worldwide each year (13000 according to the International Triathlon Union’s 2014 report).

Every triathlon has a swim component, with distances ranging from 750m for a sprint triathlon to 3800m for an Ironman. In the Olympic distance triathlon, the swim leg is 1500m, requiring an experienced swimmer to spend somewhere between 16 to 25 minutes in the water.

Who participates in OWS events?

Open water swims and triathlons are popping up everywhere. Competitions range from mega events in major cities, remote competitions and challenges in places like Antarctica, and to smaller community races. These events are not reserved for elite athletes. Many races have different age categories. Race categories can include family events, relays, tri-a-tri distances for beginners, as well as olympic, ironman, and marathon distances. There can be separate categories for people who swim in a wetsuit, and those who do not.

The Toronto Triathlon Festival (TTF) which takes place annually in mid July in Ontario, Canada is an example of a more inclusive and community oriented event. This event attracts athletes with different abilities and experience.

Inclusive OWS events also exist and have age categories for kids as young as 5yrs old. This is the case for the Sea Dogs Open Water Swim, which took place August 5th, 2017 in Little River Reservoir, Saint John, NB, Canada. Children under the age of 5 are allowed to enter a combined 25m open water swim and 200m run event.

Photo by Peter

Recreational water quality at OWS and Triathlon Events

At the 2016 Olympics in Brazil, the impact of Rio’s famously contaminated water on the health of the olympians participating in open water events made international news. There was much debate about whether or not athletes should compete in open water venues that long-term and event-specific testing confirmed to be terribly contaminated with sewage.

International and local environmental and public health organizations recommend water quality testing at the swim site is a best practice in order to protect the public health. Monitoring ensures that swimmers know the water quality before their race, and understand the risks of contracting a recreational water illness. Swimmers in these events may include people with a higher risk of becoming sick from contaminated water. Specifically, young children, pregnant women, seniors, and individuals with immune deficiencies have higher chances of becoming ill when swimming in contaminated water. Tourists are also more likely to become ill compared to locals.

Additionally, water quality testing is a best practice prior to events where participants are in contact with open water for long periods of time (for example the Manhattan Island Marathon Swim). Prolonged lengths of time in water also elevate an individual’s’ chances of becoming sick from waterborne illnesses.

Photo by Ben Lawson

OWS and triathlon event specific water quality monitoring


In 2012, 338 of the 1,100 swimmers in the Hampton Court Swim in the Thames River in London fell ill immediately after the event. Their symptoms varied from diarrhea and vomiting, to fever and nausea. Increased risk awareness for swimmers was the top recommendation by the Public Health England’s consultant epidemiologist following the 2012 event.

In order to protect the health of athletes, international and local sport and health bodies strongly recommend that event organizers aim to host events in water bodies with excellent water quality. These organizations, including the World Health Organization, the International Triathlon Union, Multi-sport Canada, and USA Triathlon, also recommend that tests be conducted prior to events to determine the venue’s water quality. It is also a best practices to determine whether an event site is vulnerable to elevated contamination from sources such as combined sewer outfalls, storm drains, sewage bypasses, and wet weather events.

However, event organizers in Canada, the US, and around the world are not required to test the water at the swim site prior to a race. Nor are they obligated to provide information regarding wet weather events and combined sewer overflows that may impact the health of the swimmers. Event organizers might give participants the municipal water quality results for surrounding beaches. This is not a best practice, as the water quality at the swim site can differ greatly from a nearby beach. A multitude of factors contribute to poor water quality, such as site specific contaminants or recent weather events.

Take, for example, the Toronto Triathlon festival, held in the inner harbour of the City of Toronto. Toronto’s inner harbour is a zone impacted by 9 combined sewer outfalls and that is vulnerable to contamination following wet weather events. Over 600 people typically enter the water for this popular event. The inner harbour is not tested by the city, nor is it tested by event organizers prior to the triathlon. Rather, the TTF references Toronto’s 11 monitored beaches, none of which are in the event zone, as a testament to the water quality in the inner harbour.

Who is responsible for recreational water testing at OWS and triathlon events?

Many event organizers (especially for elite events) do elect to test the water. Moreover, they alert swimmers if test results flag contamination. Some organizers even have a policy of cancelling or postponing an event due to poor water quality. For example, at the ITU World Triathlon Series in Montreal the organizers cancel the swim if the water fails to meet standards established by the World Health Organization (WHO) and the European Public Health Association.

Even when a swim event site is tested and fails to meet water quality, events are not typically cancelled.

There are a number of avenues for testing water at water sport events. In certain cases, when an event takes place at a regularly monitored beach or swim spot, event organizers may refer to the environmental health officer or established monitoring body’s test results and recommendations.

Where no monitoring exist it falls on the event organizers to evaluate the water quality. Event organizers are challenged by the cost and logistics of water quality testing. In the United Kingdom, the organization Swim Safety provides water quality testing and analysis services for many OWS and triathlon events. Organizers test according to the EU bathing water directive standards and BTF/ITU regulations. Many events opt to work with the local monitoring body, such as the public health unit, to evaluate the water ahead of a race.

People are increasing participating in OWS and Triathlon events. As a result, water quality monitoring, as a best practice, is becoming more commonplace. Water quality testing informs people whether or not the water failed to meet recreational water quality standards. With this information OWS and triathlon participants can decide whether or not to take the plunge.

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