State officials said on Saturday that small amounts of harmful blue-green algae have led to testing at a western Ohio reservoir.
A sign warning swimmers not to swallow the water at Clarence J. Brown Reservoir in Buck Creek State Park was posted.
An Ohio Department of Natural Resources spokeswoman said the toxin levels were not enough to issue a public health advisory for the body of water.
The Dayton Daily News reported that the park north of Springfield attracts about 380,000 people annually for boating, swimming, fishing and camping.
Officials said testing of the reservoir would continue.
Toxic algae has caused problems in recent years for Grand Lake St. Marys, the state's largest inland lake. An algae bloom there in 2010 forced officials to urge visitors not to touch the water or eat fish from it.
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