PORTAGE, Ind. (WLS) -- Dead fish and toxic chemicals in the water have caused several beaches in Northwest Indiana to close, including parts of the Indiana Dunes National Park.A steel plant belonging to ArcelorMittal is accused of dumping toxic levels of cyanide and ammonia-nitrogen in the Little Calumet River in Portage, according to state officials.According to the Indiana Department of Environmental Management, ArcelorMittal exceeded the daily maximum total for cyanide and ammonia nitrogen release. The department, which is leading the investigation, has requested ArcelorMittal help clean up the spill and monitor the river's chemical concentration.The National Park Service said the water out to 300 feet at the national park's Portage Lakefront and Riverwalk beach area has been closed since Wednesday. Portions of the Little Calumet River were closed between Highway 149 and 249, the park service said. The trails remain open.At the Sammie Maletta Public Marina, the sun set Friday on scores of dead fish."The odor is unbelievably bad because they decay pretty quickly," said harbormaster Barb Lusco. "So the odor is just awful. You can't stand it."The Arbin family drove up from Indianapolis for a vacation Friday, only to find the beach at the Portage Lakefront closed."It's very disappointing," said Ashley Arbin. "Well, the kids wanted to swim and play in the sand."But some residents weren't too surprised."We have always lived in this area and grown up with mills," said Vicki Mason, a Portage resident. "My husband worked at U.S. Steel so I guess we kind of know what happens here."Bruce Rowe of the Indiana Dunes National Park said the area is closed to protect public safety."Of course, we want to keep people out of the water here until we really know what's in there and what the effects might be," Rowe said.In a statement, an ArcelorMittal spokesman said the steel production company is "committed to environmental compliance and takes both situations very seriously."The effects of the spill, which reportedly could have happened as early as Wednesday, are already being seen.Marquette Yacht Club member Janice McMullen said she saw fish dying right before her eyes."I seen all the fish swimming in circles, going belly up and it wasn't like a couple. I looked around. They were up on the shores. They were everywhere," McMullen said.The mayor of Portage has criticized the Indiana Department of Environmental Management along with the steel company, saying that they knew that there was a problem and were slow in notifying the city."IDEM needs to be held accountable to let our residents and our visitors know what's going on," Mayor John Cannon said. "This is the middle of summer. This is the height, the peak of fishing season."Both the state agency and the company haven't responded to the mayor's remarks.In the meantime, officials with nearby city of Ogden Dunes say their drinking water is OK, despite concerns from some residents.State officials said they do not want anyone going into the water or eating any fish from the water until their investigation reveals more details. They said the beach could potentially reopen in a day.