SHOREVIEW, Minn. - Officials with the Minnesota Department of Natural Resources are trying to determine what killed hundreds, maybe thousands, of fish in Lake Owasso.

"Fish pathology can be very complex," said DNR fisheries manager Brad Parsons. Sometimes you find the cause, sometimes you don't."

DNR officials say there is no evidence of a chemical spill or toxins in the water. Tests show oxygen levels are normal.

"I've never seen anything like this," says Dick Zaun, who lives on the lake. "I'd like to see the lake maintain a healthy fish population, this is sad."

Lake Owasso lies within Shoreview and Roseville in the northern St. Paul suburbs.The DNRsays the lake is managed primarily for muskies.

"It's a great lake," says Zaun. "I'm hoping the DNR can figure something out."

The DNR says about 90 percent of the dead fish it's counted are small panfish, with a few bass and walleyes. Residents have pulled out a few dead muskies, too.

"It's very hard to diagnose," said Parsons. "We had people out there today and over the weekend. We want to know what's going just like everyone else."

Parsons did say that fish kills can sometimes be "a natural part of our cycle."