This weeks blazing sun has led to a sharp rise in the bacteria that causes toxic algae blooms in New Jersey lakes.

An advisory has been issued for the Crescent Cove area of Lake Hopatcong by the New Jersey Department of Environmental Protection after water tests showed high levels of Cyanobacteria.

Cyanobacteria is the organism that causes Harmful Algal Blooms (HABs) and exposure can cause a variety of health problems in both humans and animals.


People can develop a rash just from coming in contact with the contaminated water. If the water is swallowed, mouth blisters, sore throat, abdominal pain, nausea, headaches and diarrhea can occur.

Animals can also develop similar symptoms.

The DEP recommends closing the beach at Crescent Cove, but the final decision will come from local officials after consultation with the Sussex County Department of Health.


Toxic algae has been devastating for Lake Hopatcong and tourism in recent years. In 2019, the beaches were closed for most of the Summer.

Mitigation efforts have been implemented, and local officials say they are having a positive result, but it will take time for the desired results to be achieved.

Hopatcong is not the only lake effected. HABs have been detected in nearly every lake in New Jersey at some level.

A growing global problem, harmful algal blooms are not caused by true algae but rather by cyanobacteria that in many ways resemble and behave like algae. These cyanobacteria naturally occur in fresh water and can proliferate to unhealthful levels in sunlight and hot weather, forming dense mats resembling pea soup or spilled paint. - DEP Website

As of Thursday morning, the DEP has issued advisories for nine New Jersey lakes, including Hopatcong.

The majority of the other lakes under advisory are used for fishing and boating, and swimming is not permitted. However, the DEP recommends not eating fish caught in areas where HABs are present.

The following lakes are listed under the DEP advisory:

  • Bellmawr Lake, Bellmawr
  • Rosedale Lake, Mercer County
  • Indian Mills Lake, Shamong
  • Lake Ceva, Mercer County
  • Lake Sylva, Mercer County
  • Daretown Lake, Salem County
  • Spruce Run Reservoir, Hunterdon County
  • Greenwich lake, Gibbstown

You can see an interactive DEP map listing results of their water testing and HABs advisories by following this link.

The DEP encourages you to report any algal blooms you may encounter. They often look like someone spilled green or blue/green paint in the water. You can report a possible bloom by following this link.

Eric Scott is the senior political director and anchor for New Jersey 101.5. You can reach him at

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