SASKATOON -- Conservation officers are investigating what happened to the fish at Humboldt Lake.

Thousands of pickerel and perch were found floating in the water and piled up along the shore.

“We think it’s winter kill,” Larry Ries, reeve of the RM of Humboldt, told CTV News.

Winter kill is caused by extreme cold temperatures, resulting in low oxygen levels for fish.

“It’s not that uncommon in Saskatchewan. But when it happens on a lake where there’s cabins and properties, it’s quite upsetting. It’s a shame,” Ries said.

Ries said most of the fish’s gills were “wide open,” which happens when a fish is needing more oxygen.

Conservation officers have taken samples of the water and fish to confirm how the fish died.

“This lake has a history of winter kill. The last one happened in 2005,” said Gord Sedgewick, a fisheries biologist with the Ministry of Environment.

Ries said it takes about two weeks to get the results and could take even longer to know exactly how much of the lake’s fish population died.

The Ministry plans to restock the lake with half a million walleye fry in 2021.