PENNINGTON — A warning about harmful algal bloom has been issued for a third New Jersey lake.

Rosedale Lake at Mercer Meadows is closed for all recreational activity after testing high for HAB, according to the Mercer County Park Commission. Bodies of water at the park's three other bodies of water remain unaffected.

Lake Hopatcong in North Jersey and the Spruce Run Recreation Area in Hunterdon County are also under advisories that urge people to avoid contact such as through swimming, wading and water sports. Fish from the affected lakes shouldn't be eaten, and pets shouldn't drink the water.

HAB occurs when cyanobacteria blooms produce a thick, bright green scum on the surface of the lake. It can also appear as “spilled paint” or “pea soup.” This appearance is often taken for granted as a normal algae bloom.

The DEP says HAB could be a result of recent heavy rainfall carrying nutrient-rich stormwater into lakes followed by spans of warm weather.

Cyanobacteria harmful algae blooms can discolor the water or produce floating mats or "scums" on surface, the DEP says. Significant blooms may harm fish and other organisms in the water.

There have been more than 30 reports of harmful algal bloom at Lake Hopatcong since June 17, including incidents of mild skin rashes. Exposure to the blooms may cause allergy-like reactions, flu-like symptoms, gastroenteritis, respiratory irritation and eye irritation.

Contact reporter Dan Alexander at or via Twitter @DanAlexanderNJ

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