Environmental stress likely cause of fish die-off on Vancouver Island

Fisheries and Oceans Canada has found that "stressful environmental conditions" likely killed hundreds of salmon and trout in the Cowichan River in mid-July. 

The die-off was discovered by people swimming near Skutz Falls in Cowichan River Park on Vancouver Island. 

It's not known exactly how many fish died, but the incident immediately raised alarms with people who look after the river.

"We were all pretty shocked," said Parker Jefferson, who lives along the river and co-chairs the Cowichan Stewardship Roundtable. 

"This has not ever been noted before, and there's a lot of eyes on this river."

Fisheries and Oceans (DFO)  collected samples and performed tests to determine the cause of death. 

In a statement this week, the department said the cause appears to be lesions found on the fish. 

These lesions tend to be caused by stress, which can be related to low oxygen and high pH levels in the water, according to the statement.

"This can potentially be caused by the decay of algal growth, which appears to be more prevalent than usual this year. Excess algal growth is often related to a combination of low flows, hot, dry weather and availability of nutrients such as nitrogen and phosphorus." 

According to DFO, stress can make fish more susceptible to disease. 

The news comes as no surprise to advocates for the river, who for years have been warning about low flows and warmer water. 

The conditions are the result of climate change and the fact that the flow of the river is controlled by a weir — a mechanism that operates like a small dam. 

Water is gathered behind the weir in winter and released in the summer to ensure constant flow. But the weir can only hold so much water — and it's not enough to meet the needs of our modern, dry summers. 

Even though the news seemed inevitable, Jefferson was wishing it were otherwise.