Rick Garringer, a conservation officer with the Indiana Department of Natural Resources, estimated 10,000 to 20,000 fish had died by Thursday afternoon and the total "could easily be twice that", reports the Associated Press.
"It's killing all the fish," Garringer said, noting the number would be higher if the river's water through Randolph County was deeper and more heavily populated.
Most of the dead fish are small, but conservation officers also have counted catfish, bluegill and bass, he told the news agency.
Rita Mangas said dead fish had washed up along the banks of the river that crosses her family's rural property about 30 miles east of Muncie.
"There's a pile and it stinks," Mangas said. "If it's in our streams, what about our wells?"
Stateline Agri Inc. applied 27,000 gallons of hog manure to a field about a mile south of Indiana 32 last weekend that washed into the river because of heavy rains on Monday, said Amy Hartsock, a spokeswoman for the Indiana Department of Environmental Management.
Heavy Rains and Hog Manure Kills 10,000+ Fish
US - Heavy rains recently washed hog manure off a farm and into the Little Mississinewa River in Indiana causing devastation to the fish life. It has been estimated that at least 10,000 mostly small fish have died in a seven-mile stretch.