The Minnesota Department of Natural Resources suspects hundreds, perhaps thousands, of fish that died in Lake Owasso last week may have been killed by excessive oxygen in the lake.
DNR fisheries specialist Donn Schrader tells the Star Tribune newly formed ice likely trapped excess oxygen in the lake, acknowledging "It's kind of a freaky thing."
Residents reported the dead fish turned up under the ice last week.
Lake Owasso is in northern Ramsey County and is among the most popular fishing lakes in the Twin Cities area. The DNR told the Associated Press Monday most of the dead fish it counted were small panfish. But residents also showed the Pioneer Press trophy-sized walleye and muskies up to four feet long.
A DNR official told FOX 9 the agency ruled out herbicides as the cause of the die off, saying it does not treat the lake for weeds.
Harlan Hiemstra, a spokesman for the agency, tells the AP "We're not too alarmed by it. It's part of a natural process." But longtime residents and anglers speaking to both the AP and the Pioneer Press say they've never seen a fish kill on Lake Owasso at the beginning of winter, and never one of this size.
Large numbers of dead fish more commonly turn up on Minnesota lakes during ice out, when fish that were victims of the oxygen depletion known as"winterkill" emerge.