(AP) -- 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.
Boaters and tourists have canceled trips, leaving cottages and camp sites empty during what normally would be a bustling Independence Day weekend. Marinas and restaurants are cutting workers, and a few have shut down for good.
Ohio Gov. Ted Strickland asked the heads of the U.S Environmental Protection Agency and agriculture department on Friday for financial and environmental assistance in dealing with the lake's water.
"We have reached a tipping point where the degraded nature of the lake is causing a significant loss to local businesses and the total livelihood of the region," the governor said in his letter.
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.
This year state environmental regulators have found a different species of algae that can produce up to seven different toxins. Water tests have shown there are low levels of two toxins that can affect the liver and nervous systems.
While this type of blue-green algae has been found elsewhere in lakes and rivers, less is known about the toxins they produce.
There are no guidelines from the federal government or the World Health Organization on how much exposure is dangerous so state regulators decided to warn people not to touch the water.
"We just don't know what's safe," said Dina Pierce, spokeswoman for the Ohio Environmental Protection Agency.
Closing public beaches or banning swimming hasn't been done because of the lack of guidelines, said Mike Helton, a spokesman for Ohio's natural resources department. "We're letting people use their own use discretion," he said.
Boating still is allowed, and the state says it's safe to eat the fish.
So far, there are no reports of anyone getting sick from the water.
Those at the greatest risk are swimmers who accidentally gulp the water and people on Jet Skis and boats who are splashed repeatedly. The spray sends particles of the bacteria into the air where it can be easily inhaled or ingested, said Linda Merchant-Masonbrink, who oversees the state EPA's monitoring of inland lakes.
There's also the potential for catastrophic fish kills with large algae blooms that rob the water of oxygen.
About 300 dead fish washed up in the algae-filled channel behind Biesel's home a week ago. "I worry about the wildlife," he said. "I watched the ducks out there, and they could hardly push through it."
How much algae covers the water varies each day depending on the weather and winds. Earlier this week, parts of the lake showed no signs of the smell or algae, but it was apparent in some areas.
For generations, the 9-mile long lake has been lined with fishing shacks and vacation cottages, but in recent years more expensive homes have been built by retirees who have relocated near the water.
Many worry that the algae outbreak will bring down their property values, and some real estate agents say potential buyers have backed out of deals.
Some residents say they've been warning politicians about the increasing pollution flowing into the lake for at least a decade. State officials say they've been meeting with farmers, asking them to cut down on the manure that makes it way to the lake.
But residents aren't satisfied. They say stricter regulations are needed on large farms, limiting when they can apply manure to their fields and how close they can plant to streams.
"It's getting to the point where somebody needs to step on somebody's toes," said Dave Meyer, a member of the Lake Improvement Association.
No matter what happens, it may take a long time to get rid of the algae and the stigma surrounding the lake.
Jason and Delarie Adams, of Chicago, spent three days at a cabin along the lake this week, not knowing about the water warnings until they arrived.
They stayed clear of the lake and kept their 1-year-old daughter's sand toys packed away. "We saw the bubbles on the water," said Delarie Adams. "It looked like dishwashing detergent."
"I don't think we'd come back," her husband said. "I mean we can't even get in the water."
Explore further: Oil from Russian trawler wreck reaches Canaries' beaches