(AP) – Some beaches along northwestern Indiana’s Lake Michigan shoreline are closed after authorities say a chemical spill in a tributary caused a fish kill.

The National Park Service said Thursday it closed the Portage Lakefront and Riverwalk beach areas at Indiana Dunes National Park as well as waters out to 300 feet.

The Indiana Department of Environmental Management says ArcelorMittal’s Burns Harbor plant released excess amounts of cyanide and ammonia-nitrogen into the Little Calumet River’s east branch, causing a fish kill noticed this week.

ArcelorMittal says in a statement that it’s investigating and will “continue to work closely with the agencies involved.”

The city of Ogden Dunes also closed its beach. Officials say the city’s drinking water wasn’t affected, but its filtration plant restricted water intake as a precaution.