Warming weather could mean more anoxic events in P.E.I. waterways, biologist says

Unless you're standing at the very edge of P.E.I.'s Trout River, near Gunn's Bridge, seeing much below the surface is probably out of the question.  

The water looks like it's been mixed with a massive jug of milk. It smells funky too — kind of like rotten eggs — and little fish are swimming as close as they can to the top.

These are all strong indicators that this estuary is what's called anoxic. 

"It is when there is low oxygen in the water," said Kyle Knysh, a surface water biologist with P.E.I.'s Department of Environment, Energy and Climate Action. 

"When there's low oxygen, fish and invertebrates and mostly anything in the water that likes breathing oxygen doesn't do very well. So they avoid an area — or, if they're trapped, [they] can die."

The P.E.I. government has been monitoring anoxic events like this for decades. For the past few years, numbers have fluctuated between 20 and 28 cases annually. 

There have been 10 so far in 2024. Knysh said that's on par with previous trends, but with temperatures reaching new heights on the Island, he expects to see an increase in the years to come.

"There's likely going to be more reports of this because of that," he said. 

"It is concerning to aquatic life."

Knysh said lots of factors can cause an anoxic event. One is heat. Warm water is already at a disadvantage because it holds less oxygen to begin with. 

Then, nutrients thrive in the heat, which attracts more organisms that breathe more oxygen and deplete the water's supply. 

"When it's warmer out we're going to be expecting that there is going to be less available oxygen," Knysh said. "There is very, very little we can do." 

But anoxic events can be short-lived. Depending on the conditions, Knysh said the situation can change quite rapidly. 

"Within a day you can just have huge shifts.... going from, like, nearly no oxygen at night to really high oxygen during the day," he said. "Many of these systems have low oxygen events every year. So there are organisms [that have] adapted to that, to an extent."