PORTER | Swimmers were allowed back into the water Wednesday afternoon at the Indiana Dunes National Lakeshore after officials determined the substance found in the water Monday was not a health risk.
Indiana Dunes State Park closed beaches to swimmers Tuesday and Wednesday morning, but visitors were told late Wednesday morning that swimming was restricted in water above their waists in part because of high waves there, representatives said.
Swimmers early Monday afternoon reported a glittery substance floating on the water near Porter Beach that left a dark, sticky film on their skin. Investigators from the Indiana Department of Environmental Management and the U.S. Coast Guard said the plume was 2 miles long and half a mile wide.
On Tuesday, IDEM reported preliminary tests showed the substance is tricalcium orthophosphate, an anti-caking agent used as a food additive and in industrial applications. A Porter plant manufactures the material and ships it out on barges but has not been targeted as the source of the material, according to IDEM officials.
Lab tests by the United States Geologic Survey and the Indiana Department of Environmental Management determined Wednesday the substance was not a health threat, according to a press release from the Indiana Dunes National Lakeshore. The substance also included an increased amount of natural products such as algae and mica particles.
Officials are still trying to determine how the substance ended up in the water.
U.S. Coast Guard investigators pored over a week of logs at the Port of Indiana on Tuesday and ruled out vessels passing through as a source. Nearby ArcelorMittal also was ruled out as a source, according to the Coast Guard.
Times staff writer Elvia Malagon contributed to this report.