With less than a week until the Fourth of July, people heading to Lake Hopatcong are being told to stay out of the water.
Swimming, boating, and all other activities are now banned because of a dangerous algae growing quickly in the hot weather.
The state Department of Environmental Protection says the algae bloom is a convergence of nutrient rich algae that gets caught in the lake with the rain water. MORE: State: Don't swim in Lake Hopatcong or even touch the water
The algae can cause rashes, and several people have already gotten mild skin rashes from just touching the water. It can also cause flu-like symptoms and even respiratory irritation.
Officials say the state police and the sheriff's office will be patrolling this weekend to make sure no one is in the water.
The DEP says the issue could take months to clear up.