Patches of green and turquoise slime floated like thick paint in the channel behind Kyle Biesel’s home. His pontoon boat sat covered up, unused for weeks, on a wooden lift stained by the algae.

A foul smell enveloped the backyard where he used to fish and watch blue herons glide over the water. He called it a “sickening combination of manure and propane gas.”

Even more alarming, tests reveal that the waters in Ohio’s largest inland lake contain dangerous toxins with the potential to cause rashes, vomiting or even liver and nerve damage. State officials say it’s no longer safe for swimming and skiing.

It’s causing economic and environmental distress for hundreds of people who work along Grand Lake St. Marys in western Ohio, an area already hurt by manufacturing cuts that have contributed to Ohio’s highest unemployment rates in a quarter century. Tourism brings an estimated $216 million into the area with much of that coming from visitors to the lake.

“People are scared to death,” said Chuck Black, who manages Windy Point Marina. “You can look out on this lake and count the boats on one hand.”

Boat repairs are the only thing keeping Black in business because gasoline sales are down by more than half and could cost him well over $50,000 this year. He now wears waterproof boots when he’s fixing boats after getting a rash when water dripped on his feet.

This is the second straight summer of water warnings along what locals call “Ohio’s other Great Lake.” The water problems led to a drop in visitors last year to 687,000, down from about 737,000 a year earlier.

It’s likely to be even worse this summer.

Grand Lake St. Marys is one of the state’s most lakes polluted because of the fertilizer and manure that runs off from nearby farms and into creeks and streams flowing into the lake, feeding the algae that produces toxins.