Alberta Health Services is advising people not to swim or wade in the Elbow River within the city of Calgary.
“Elevated levels of fecal coliforms were detected via routine testing of the river water,” AHS said in a press release Friday afternoon.
The affected area stretches from 25 Avenue S.W. to 9 Avenue S.E..
Doctor Jason Cabaj, the medical officer of health for Calgary, said elevated bacteria levels were first noticed last August 2015 and AHS has been monitoring levels since then.
There is no direct source or explanation for the high levels of coliforms.
Cabaj said it could be a combination of human and animal use of the river, storm water emptying into the river from several outfalls along the river bank, plus the hot temperatures and the low water levels.
AHS warns against drinking the untreated river water. It said water-borne organisms, including fecal coliforms, can cause vomiting and diarrhea.
Officials also suggest skin, ear and eye infections can result from any contact with Elbow River water at current contamination levels.
AHS is posting warning signs at common river access points.
Environmental Public Health officers will continue to monitor the water.