The swim area at Kettletown State Park remains closed due to blue-green algae.  The beach in Southbury has been closed for nearly three weeks.  The blooms can produce a toxin harmful to people and pets if ingested, or can cause irritation. The state Department of Energy and Environmental Protection said in a weekly water quality report that Kettletown has a shallow cove that traps the blue green algae, which thrives when there are hot temperatures and thunderstorms that wash nutrients into the water.