DNR investigating extent of fish winterkills in Minn. lakes

Hundreds of dead fish are appearing as the ice melts on some Minnesota lakes this spring.

Jerry Johnson, DNR fisheries supervisor for the east Twin Cities metro, said it's one of the worst years in decades for a phenomenon called "winterkill." Large numbers of fish can suffocate on lakes covered in snow and ice.

"If you put a number of people in an airtight room, they would eventually run out of oxygen," Johnson said. "Well, a lake is, during ice up, it's the same concept. You're actually cutting off the system from oxygen and it then becomes a function of how much oxygen is stored in that area and how fast it's being used."

Johnson said shallow lakes are most at risk for fish kills during winter months. He said the condition is worse when lakes ice up early in the season and when there's an early, heavy snowfall.

DNR fisheries managers are working to assess just how many lakes experienced "winterkill" this year, but Johnson said the problem is widespread.

"We'll be busy trying to determine what lakes have experienced winterkill, [and] busy determining the extent of the winterkill," he said. "We'll try and determine what we need to replenish or reintroduce."