A water protection group on P.E.I. says more needs to be done to prevent the Island's rivers from become anoxic.
The problem is particularly bad this year because of the unusually hot weather, which encourages algae growth.
Excessive nutrients in rivers start a chain reaction. Algae grow in huge masses, then die. As algae rot, oxygen is consumed in the water, a condition known as anoxia.
These anoxic events can go on for days or weeks.
The river turns green and stinks.
When oxygen levels get too low, it's hard for anything to survive in rivers that go anoxic.
However, provincial biologists worry it'll happen more often this summer because rivers are low and warmer than usual.
Recent rain has actually made the problem worse, because fertilizer could run off into the rivers, and those nitrates can speed up algae growth.
The Hunter-Clyde Watershed Group is asking the provincial and federal government to help protect waterways.
Residents have complained about odour coming from the river, and some say it's worse than previous years.