Fish kills reported in Buffalo Lake and Yahara River

The state Department of Natural Resources said it is investigating reports of fish kills in the Buffalo Lake watershed near Montello, which covers parts of Marquette, Green Lake and Columbia counties about 65 miles northeast of Madison, and in the Yahara River in Stoughton.

The DNR said in a statement that a combination of natural processes and environmental conditions can lead to reduced oxygen levels, which in turn can be harmful to fish.

“Additional reports of fish kills are likely, and the DNR will continue to investigate reports as they come in,” the department said. “When a body of water has widespread low dissolved oxygen levels and there is no deeper, cooler water for fish to move to, it can result in fish kills.”

On Buffalo Lake, a large number of dead fish were reported to the DNR on July 10, and an investigation began the next day. Fish biologists sampled several locations in the more than 400-square-mile watershed and confirmed low dissolved oxygen levels in the upper basin and some tributaries.

The event likely affected all fish species in the watershed, and the DNR warned that boaters and anglers on Buffalo Lake may encounter pockets of dead fish. So far, no dead fish have been reported in Puckaway Lake, but that could change in the coming days as water moves down the Fox River.

“There have been reports of stained or tea-colored water, and this is likely caused by tannic acids, a byproduct of decaying vegetation, released from flooded wetlands,” the DNR said. “In addition to the color changes, the public may notice an oily sheen on the lake surface, which occurs when bacteria consume excess iron in the water.”

The second reported fish kill occurred on the north shore of Stoughton on the Yaraha River, which flows through Lakes Mendota, Monona, Waubesa and Kegonsa before continuing south to Stoughton.

A Facebook post Wednesday on the Madison Chain Fishing Club page appeared to show blue-green algae and dead fish floating in the river near a bridge near North Division and Forton streets. The DNR had no immediate information about the deaths, but the Facebook post said the dead fish included bluegill, largemouth and smallmouth bass and northern pike.

Anyone who sees a large number of dead fish is asked to call the DNR hotline at 1-800-847-9367. People should not attempt to pick up or handle dead or dying fish, and anglers and their pets should not eat dead or visibly dying fish.