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Posted Monday, September 23rd, 2019

About 60 Percent of Lake No Longer Under Algal Bloom Advisory

The New Jersey Department of Environmental Protection today lifted harmful algal bloom advisories for additional areas of Lake Hopatcong, bringing to about 60 percent the total area of the lake no longer under water recreation advisory.

DEP monitoring indicates that cell counts for cyanobacteria, the organism causing the blooms, have fallen below the state’s Health Advisory Guidance level at the mouth of Woodport Bay, east of Davis Cove Mid-Lake, and the Bertrand Island area (see map below).

DEP Lifts Large Portion of Lake Hopatcong Water Recreation Advisory

Areas that remain under advisory are the Mid-Lake area in the lower-central portion of the lake, the Prospect Point and Woodport Bay area in the northeastern arm of the lake, the Crescent Cove/River Styx Area, and the area adjacent to Hopatcong State Park.

Recreational users are reminded to avoid swimming or coming in contact with lake water in these areas until monitoring demonstrates that cell counts fall below the Health Advisory Guidance level.

“We realize that this has been a frustrating season for the residents, business owners and visitors to this beautiful lake,” said DEP Commissioner Catherine R. McCabe. “Our primary goal throughout has been to ensure the protection of public health, especially for vulnerable populations such as children. The DEP remains committed to better understanding the causes of these blooms and solutions to reduce them in the future.”

Harmful algal blooms are caused by bacteria that in many ways resemble and behave like algae. The causes of the Lake Hopatcong bloom this summer are not fully understood. However, harmful algal blooms are generally fueled by nutrient-laden stormwater runoff followed by periods of hot weather that cause the proliferation of these bacteria, which are naturally present in waterbodies.

Under these conditions, blooms can reach levels that can be harmful to people and to pets coming in contact with the water. They typically subside with the onset of cooler weather.

For more information, including Lake Hopatcong monitoring results and maps, visit