CHICAGO (CBS) — Environmental authorities in Indiana said preliminary results have found that an additive used in food and fertilizer and a metal cleaning agent were in the slick found on the lake this week. Someone who spends a lot of time on the lake doesn’t believe it was an isolated incident.

“It’s been a dirty week for Lake Michigan,” said Basil Tydings, an East Coast transplant who lives in the Chicago area because of the lake.

WBBM’s Mike Krauser reports Tydings is a surfer and stand-up paddleboarder who spends a lot of time on Lake Michigan, including at the Ogden Dunes in Porter County, Ind.

“Sometimes the lake water tastes like the air smells,” he said.

Indiana state officials banned swimming along parts of the lakefront and advised swimmers of possible contamination, after a slick first believed to be oil was spotted near Porter Beach on Monday. Officials later determined the substance was a combination of D-gluconic acid, which is used as a metal cleaner, and tricalcium orthophosphate, an additive in food and fertilizers.

Officials have said it’s not highly toxic, and they were working to determine exactly where it came from. The Indiana Department of Environmental Management said a nearby manufacturer makes tricalcium orthophosphate, but it was not clear if that company was the source.

Steel mills and refineries are located east and west of the beaches in Porter County.

“They need the industry for the jobs, and so forth, but this is a precious, precious jewel, this Lake Michigan,” he said. “There are some drains that I wonder what is draining out of those places into the lake.”

Tydings said has paddled through several slicks on the lake, and he said he became ill last week after surfing at Ogden Dunes.

“Real bad headaches and real tightness on the sides of my head,” he said. “I was like, ‘Wow, what’s going on?’”

Those symptoms were likely the result of E coli contamination in the late due to runoff from last week’s storms.

Tydings said visitors have to be careful on the lake; you never know.

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