When is your water clean enough to swim?

As the calendar pages flip into fall, Edmontonians are soaking up the last bit of summer by taking advantage of the remaining warm temperatures and a new swimming beach in the heart of the city.

"Accidental Beach"-a one kilometre sand bar on the south side of the North Saskatchewan River-became a welcome surprise as a result of construction of the new Tawatina Bridge. And while it's resulted in a new place for residents to spend the day in and around water, it has others wondering whether the river is safe to swim.

Nick Ashbolt, School of Public Health professor and international water expert, weighs in with three things to be aware of before you take a dip.

1. Rain

Do not swim or have body contact with the river during or up to a few days after a heavy rainfall.

"During a heavy rainfall and after untreated sewage enters the North Saskatchewan River via storm water drain outfalls," explains Ashbolt. "The sewage enters upstream and through the City of Edmonton-right where you'll be swimming."

2. Brown or murky water

Avoid being in the water when it appears very brown or cloudy.

"When the water is highly turbid-brown with suspended matter-then there is a higher likelihood of associated fecal matter and disease-causing viruses," says Ashbolt. "These pathogens can cause diarrhea, stomach upsets and fever symptoms, so avoid water contact on these days."

3. Rely on more than E. coli levels

The traditionally measured Escherichia coli (E. coli or fecal coliforms) levels alone are a poor indicator of health risks, so it's important to not rely solely on these tests for whether it's safe to be in the water.

Alberta Health is piloting newer monitoring tools that are based on United States Environmental Protection Agency and School of Public Health research that tests for other types of fecal source indicators- as sewage not animals are the major source of human infectious viruses in waterways.

"We've been able to identify other markers-for human sewage and cattle manure-which, in addition to E. coli, focus on human viruses and animal pathogens associated with stomach upsets in swimmers," says Ashbolt.