The state Department of Health and Human Services said in a news release Friday that the alert is for toxic blue-green algae at Kirkman’s Cove Recreation Area.
Samples taken earlier this week at Kirkman’s Cove were above the state’s threshold.
Officials say the alert will continue at the lake for at least two more weeks because testing will require two consecutive weeks.
The alert means designated swimming beaches are closed. Recreational boating and fishing, as well as camping and other outdoor activities, are still permitted.