ESCANABA (AP) — Michigan officials are investigating a fish kill that affected a dozen species on the middle branch of the Escanaba River in the Upper Peninsula.

The die-off was reported Aug. 9 on the 52-mile-long river, which is popular with anglers, officials said Wednesday.

It happened near Gladstone, downstream of Verso Corp.’s Escanaba Paper Mill, which the previous week had reported the rupture of a pipe at its wastewater treatment plant.

“The pipe failure has been corrected and outflowing water quality is improving, with test results pending,” Jay Parent, district supervisor for the state Department of Environment, Great Lakes and Energy’s Water Resources Division.

Numerous fish were killed, including panfish, walleye, northern pike and largemouth bass, the Michigan Department of Natural Resources said.

The affected area is a three-mile stretch between Dam No. 2 and the river mouth, said Tom Asmus of the water resources division. Both agencies are monitoring water quality in the area, he said.