More than 100 turtles were discovered dead both in and along a short stretch of the Minnesota River in a western Minnesota wildlife refuge.
Law enforcement officials with Big Stone National Wildlife Refuge - an 11,586-acre protected natural site located about 70 miles west of Willmar - were alerted to the mysterious die-off on April 30, said Tina Shaw, public affairs specialist with USFWS Midwest.
The turtles were discovered both in the water and on the riverbank along a half-mile stretch of the Minnesota River. Staff at the refuge believe 100-200 turtles may have died, though Shaw noted they are still collecting specimens, so the final count might change.
So far, they have discovered both painted and snapping turtles among the dead, but because the investigation is in progress, they may discover more species.
What killed the turtles isn't yet clear. Shaw said some of the collected turtle specimens were sent to the USGS National Wildlife Health Center in Madison, Wisconsin, for testing.
Painted turtles are the most common turtle species in the region, the Minnesota DNR says, and are often referred to as mud turtles. Snapping turtles, meanwhile, were previously listed as a species of special concern due to reduced numbers. They were delisted in 2013 though after changes to the state's commercial turtle harvesting rules.