Ontario Beaches are posted with warnings of possible health risks when elevated Escherichia coli (E.coli) densities are present. The recreational water quality guideline of 100 E.Coli per 100 ml of water is set jointly by the provincial ministries of Environment and Health.

Escherichia coli are bacteria present in the droppings of virtually all warm-blooded animals and are the indicator bacteria for fecal contamination of surface waters.

Generally, it is up to the Medical Officer of Health for the local Health Unit to decide when a beach should be posted. Once a beach has been posted for elevated E.coli levels, more frequent water samples are taken by the Health Unit. Beach Postings are removed after E.coli levels decrease to acceptable levels.

Monitoring of beach water quality for public health is the responsibility of the local Health Unit.