ODESSA, Minn. — The cause of a turtle die-off along the Minnesota River in the Big Stone National Wildlife Refuge in western Minnesota remains undetermined at this time.

The first report of dead turtles came April 29. Visitors reported seeing dead turtles in the water and on the riverbank along an approximate half-mile stretch of the Minnesota River. Staff at the refuge estimated 100 to 200 turtles died.

Staff collected decomposing turtles and sent samples to the U.S. Geological Survey National Wildlife Health Center in Madison, Wis., according to Tina Shaw, public affairs specialist with the U.S. Fish and Wildlife Service in Bloomington.

She said the laboratory found bacterial activity in the samples provided, but the results are considered inconclusive, partly because the samples were greatly decomposed. Further viral testing is underway at this time.

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It will likely be another couple of weeks before more is known, she said.

The dead turtles included both painted and snapping turtles of various sizes.