Blue Marsh Lake - Hazardous Algae Bloom Warning and Closure

USACE Philadelphia District
Published Aug. 26, 2021
Hazardous Algae Blooms Warning Sign (August 2021)

Hazardous Algae Blooms Warning Sign (Blue Marsh Lake August 2021)

The U.S. Army Corps of Engineers’ (USACE) Philadelphia District is advising visitors to   Blue Marsh Lake to be aware of the presence of extremely high levels of blue-green algae in the lake and the potential for harmful toxins to be present. Due to the high levels of algae in the lake, the Swim Beach at the Dry Brooks Day Use Area will be closed. Additionally, visitors are advised to avoid contact with the lake water until further notice.

USACE has been working with the Pennsylvania Department of Environmental Protection to conduct sampling and testing at different locations at Blue Marsh Lake. Test results have indicated high levels of blue-green algae and the potential for harmful toxins produced by these algae.

Heavy rainfall and significant runoff convey nutrients to the reservoir. When followed by hot weather, blue-green algae can thrive and multiply. Blue-green algae, also known as cyanobacteria, are microscopic organisms found naturally in all types of water. In warm, nutrient-rich environments, cyanobacteria can multiply quickly, creating blooms that spread across the water’s surface. These blooms can create toxins that are harmful to humans and pets.

To protect yourself, your family, and your pets from blue-green algae blooms:

  • Avoid water contact in areas where the water is discolored or where you see foam, scum, or mats of algae on the water’s surface.
  • Children and pets are especially susceptible to the harmful effects of the toxins produced by blue-green algae. Do not allow children or pets to play in or drink scummy water.
  • If you have contact with water that might contain harmful cyanobacteria, rinse off with fresh water as soon as possible afterwards
  • Learn more about Harmful Algae Blooms and their associated risks by visiting or

USACE will continue to conduct testing at different locations at Blue Marsh Lake and provide updates appropriately. For additional  information, please contact the Park Office at 610-376-6337.

Scott Sunderland
Bri Treichler

Release no. 21-022