Visitors are instructed not to swim, wade, play in or drink the water in the swimming area at the Sussex County park.
Pets and animals should also refrain from any contact with the water, and fish caught from the area should not be eaten, the DEP said.
Cyanobacteria (blue-green algae), are naturally present in streams and lakes, and are responsible for the majority harmful algae blooms, the DEP said. They can produce toxins that are dangerous for people and animals.
Duck Pond Trail and sections of Spring Lake Trail are also temporarily closed due to flooding.
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