Hundreds, possibly thousands of crappie, walleye, bass and muskie were found in November, belly-up under the ice in Owasso Lake, Shoreview, Minnesota. One of the muskies even measured 48 inches long!
Shoreview homeowners thought low water levels from the recent drought caused low oxygen levels which killed the fish.
Rumors also spread that aquatic herbicides used for lake weed treatment were the culprit. The DNR did confirm individual permits are issued to lakeshore property owners for aquatic weed control however, the last treatments were made in August, and had no affect on the fish after treatment.
A spokesman for DNR also stated there was no evidence of a chemical spill or toxins in the lake.
“Usually lack of oxygen in winter causes fish kills” said Donn Schrader, Department of Natural Resources fisheries specialist. “In this case it looks like oversaturation of oxygen in the fish killed them.”
Samples of water taken from Lake Owasso showed oxygen levels extremely high at 14 parts per million. Normally, dissolved oxygen in water is a positive sign and low levels are a sign of severe pollution. The dissolved oxygen level must be at least 5 parts per million to support most fish & aquatic organisms. As dissolved oxygen levels in water drop, fish are put under stress.
Aquatic vegetation and algae produce oxygen. In this case, Lake Owasso froze very rapidly. This rapid freeze trapped oxygen under the ice. Clear ice allowed sunlight to cause weeds and algae to continue growing and emit additional oxygen. This extreme increase in oxygen under the ice killed the fish.
Weed and algae control by chemical (www.killlakeweeds.com) or physical removal (Weed Razer & Water Weed Rake) would have eliminated the fish kill problem. By reducing the amount of weeds and algae, the oxygen level would have been reduced in the frozen lake. This would provide a healthier environment for all aquatic life including fish.
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