The discovery of hundreds of dead mackerel washed up on the shore of Cape Breton’s Bras d’Or Lakes has residents and environmentalists worried.

Annette Coffin has been living on the shores of the lake for more than a year, but last week she saw something she’d never seen before.

“There were lots of shiny things in the water. Hundreds of shiny things,” Coffin said.

She said the discovery of the dead fish made her immediately concerned.

“I swim in this water, and I live on this water, and we’re on a protected lake, environmentally,” Coffin said.

Department of Fisheries and Oceans officers were in the area on Tuesday collecting samples, but a spokesperson said the officers noticed no abnormalities in the fish they collected.

The Bras d’Or Lakes were completely frozen this time last year, but currently they’re iceless, open water — a fact that speaks to the changing weather patterns in the region, some experts say.

“The ocean climate is changing, and it’s changing at an accelerating rate,” said Bruce Hatcher, chair of marine ecosystems research at Cape Breton University.

Hatcher, who studies the Bras d’Or Lakes, said he believes the fish died of natural causes.

“These fish made a mistake, they made an error of judgment,” Hatcher said.

“They were fooled by the weather, would be my guess,” he said.

With above-average water temperatures in the lake this winter, the fish may have been trapped in the shallow water as the temperature dropped, Hatcher said.

“Except for managing our greenhouse gas emissions and trying to slow down the warming of the planet, we are not at fault,” he said.

A spokesperson for the Department of Fisheries and Oceans said bacterial testing on the fish came back negative, while viral testing is ongoing.

With files from CTV Atlantic’s Sarah Ritchie