Open Water Data

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:

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

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.



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.


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.


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:

Data Sources

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.