E. coli Level
E. coli is a bacteria that can cause illness in humans and animals. Water can be tested for E. coli and test results are typically available about 24 hours after samples are collected. Results are expressed as Most Probable Number (mpn) of E. coli per 100 ml of water.
This website provides mpn results and color indicators that are easier to understand:
- PASS - A water site is marked green and PASS when the geometric mean of 5+ samples is equal or below 100 mpn of E. coli per 100 ml of water, which is Toronto's beach water quality standard and the most rigorous in the world. If only a single sample is available, PASS means equal or below 200 mpn of E. coli per 100 ml of water.
- FAIL - A water site is marked red and FAIL when the geometric mean of 5+ samples is above 100 mpn of E. coli per 100 ml of water. If only a single sample is available, FAIL means above 200 mpn of E. coli per 100 ml of water.
- UNKNOWN - A water site is marked grey when there are no results or there is no available information.
NOTE: It is important to note the date the E. coli level was collected. E. coli levels can change significantly from one day to the next as environmental conditions change. To avoid misleading people, when results are from more than 8 days ago, PASS and FAIL indicators will display in grey as OLD PASS and OLD FAIL.
Common Causes
- Combined Sewer Overflows (CSOs) - Heavy rains and high water levels can lead to increased E. coli levels, especially in bodies of water near municipalities with CSOs, such as Lake Ontario in the Greater Toronto Area. It is generally recommended to avoid swimming in these areas 24-48 hours after a heavy rain. Overflows can also occur during dry weather, so check E. coli levels on this site or from other sources whenever possible.
- Heavy Rain - Stormwater runoff can carry animal droppings on the ground into local streams and lakes, causing elevated E. coli concentrations. Additionally, rain can cause soil erosion and higher turbidity (poor water clarity). Bacteria can be killed by sunlight, so having low water clarity reduces the chances that bacteria in the water will be exposed to sunlight and die.
- Birds - High concentrations of birds, such as where you will find Canada Goose and Seagull droppings, can also increase E. coli levels. It is generally recommended to avoid swimming in areas around high concentrations of birds.
Possible Illness
There is no way to say for sure whether or not you will get sick if you go into water that has a high E. coli level, but you will have a higher chance of getting sick. The risk of getting sick is higher if you swallow water or get water in the nose, eyes, ears or an open wound. Examples of possible illness include stomach upset, ear infection, sore throat, or wound infection.
Health Canada estimates that there will be 10-20 illnesses for every 1,000 people who swim in waters that meet government guidelines. That rate of 1-2% is considered an acceptable level of risk by government officials. Once bacteria levels exceed government guidelines, the risk of contracting an illness increases.
Guidelines
Toronto
Toronto’s beach water quality standard is a geometric mean concentration (minimum of five samples) of less than 100 mpn per 100 ml of water, which is the most rigorous standard in the world.
Ontario
In 2018, the recreational water quality standard in Ontario is a geometric mean concentration (minimum of five samples) of less than 200 mpn, and a single-sample maximum concentration of less than 400 mpn. The previous standard was less than 100 mpn as a geometric mean. It was made less strict in order to hamonize with national guidelines. For more information, see Ontario Ministry of Health Changes E. coli Measurement Standard at Beaches.
Canada
The Guidelines for Canadian Recreational Water Quality recommends the use of two limits for E. coli. A geometric mean of ≤ 200 mpn based on the previous five samples or a single sample limit of ≤ 400 mpn.
United States
Each state has its own water quality standards, but acceptable E. coli levels are roughly inline with Canada. For example:
- New York: A geometric mean of < 126 mpn or < 235 mpn for a single freshwater sample, < 104mpn for a single saltwater sample.
- Michigan: A geometric mean of < 200 mpn or < 300 mpn for a single sample.
Data Sources
- City of Toronto - Every year between June and September (Labour Day), the City of Toronto’s Parks, Forestry & Recreation division collects daily water samples from Toronto’s supervised public beaches to be tested for E. coli bacteria. Toronto Public Health (TPH) measures E. coli levels to determine the beach water quality for public swimming. Results are posted to the Beach Water Quality page and this site is updated based on the Beach Condition Data.
- Swim Drink Fish - Works at the confluence of water, people, and storytelling, using community science, technology, and communications to connect people to water. Through a network of Community Water Monitoring Hubs, Swim Drink Fish gathers and shares water pH, Chlorine, Alkalinity, Dissolved Oxygen, Hardness and E. coli levels. Results are posted as soon as lab results are available, and this site is updated based on the Lake Ontario Waterkeeper Toronto Monitoring Hub.
More Information
E. coli, more formally called Escherichia coli (Wikipedia), is a bacteria commonly found in the lower intestine of warm-blooded organisms. High counts of E. coli in recreational water may increase the chances of gastrointestinal illnesses and skin/eye infections.
The following links provide additional information related to E. coli in recreational water.