The analysis from the group Environment America shows Indiana dumped more than 17 million pounds of pollutants into its waterways in 2012, more tonnage than any other state.
14 million pounds – or about four-fifths of the pollution were released by just one place, the AK Steel Foundry in Rockport.
But the report only uses self-reported government data which leaves out industries such as oil and gas and agriculture. And Indiana Office of Water Quality Assistant Commissioner Bruno Pigott says water quality isn't measured that way.
"We don't measure releases to the environment when we're determining water quality," Pigott says. "We look at the concentrations and discharges from water treatment plants."
But John Rumpler, one of the report's authors, says even though there are other numbers to consider and Indiana fares slightly better when considering the types of pollution in the water, the state still isn't doing enough to police polluters.
"And I would submit that the data for Indiana is alarming on either scale," Rumpler says.
The state falls to 15th worst in the nation when considering the toxicity of the chemicals released.