The Nebraska Department of Environmental Quality found elevated toxin levels at Willow Creek Reservoir in Pierce County due to blue-green algal blooms.
Willow Creek will continue to be under the alert until it passes two consecutive weeks of testing.
Signs have been erected at Willow Creek warning the public. Swimming beaches have been closed. Recreational boating and fishing can continue. The public is cautioned against getting in the water of swallowing the water.
Pets should be kept out of the lakes and should not be allowed to drink from the lakes.
Camping and picnic areas remain open. Outdoor activities are permitted.
State officials monitor all 52 public lakes in Nebraska throughout the recreational season. Sampling results are updated every Friday.