NJ lake officials worry about heat wave impact on water quality

The conditions of North Jersey's ongoing heat wave, apart from causing discomfort for many residents, could pose trouble for area lakes that have already been plagued by environmental problems in recent summers.

Lake Hopatcong and Greenwood Lake have been temporarily closed multiple times in the past few years due to the presence of harmful algal blooms, or HABs. The bloom concentration has not risen to a level that prompts closures this year, but officials are concerned that could change soon if the heat does not subside.

"We are holding our breath," said Marty Kane, chair of the Lake Hopatcong Foundation, in an interview with NorthJersey.com on Wednesday afternoon. "Mother Nature is not helping us right now."

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What are harmful algal blooms?

HABs are caused by cyanobacteria that occur naturally in freshwater, forming dense mats that resemble pea soup or spilled paint, according to the New Jersey Department of Environmental Protection. The bacteria can cause numerous symptoms in humans if ingested, including headaches, sore throat, nausea and diarrhea, while direct contact with the algae may result in a skin rash.

The blooms are more likely to grow in water that is still, warm and nutrient-rich, all properties that are exacerbated by prolonged periods of hot, sunny weather.

Kane said he is keeping an eye on New York, where several beaches in Westchester and Putnam counties closed due to the blooms within the past week. Recent readings have measured Lake Hopatcong water samples at 86 degrees, he said, and "my guess is we're probably going to set records for the water temperatures this summer."

An interactive map on the DEP website shows more than a dozen samples taken from various parts of Lake Hopatcong over the past month that indicate a HAB watch, triggered when the cyanobacteria concentration is between 20,000 and 80,000 cells per milliliter. An algae "advisory" goes into effect past the 80,000 threshold, during which the DEP recommends the closure of public beaches and warns the public to avoid water contact.

The highest reading at Lake Hopatcong this year was 67,125 cells per milliliter taken from Skytop Road on May 31. The most recent posted samples, a series of readings on July 2, yielded a maximum concentration of 50,750 cells per milliliter at the Hopatcong State Park beach.

Past closures at NJ lakes

Beaches at Lake Hopatcong and Greenwood Lake were forced to close for much of the summer in 2019 due to repeated high HAB concentrations. The blooms returned for parts of 2020 and again in 2022, and though not as severe, officials began consulting with environmental experts on ways to prevent the bacteria from forming.

Lake Hopatcong will undergo alum treatment in the fall, a short-term method that reduces the amount of phosphorus in the water allowing blooms to grow. The more long-term solution, Kane said, is a large-scale aeration system that diffuses oxygen into the bottom of the lake to break up algae.

Kane and his colleagues at the Lake Hopatcong Foundation and similar organizations throughout the state have implemented various treatment plans designed to prevent HABs from appearing. What they could really use right now, though, is a few days of cooler weather.

"We're hoping we've done enough," Kane said, "but these are the worst possible conditions for algal blooms."

Anyone who observes a suspected HAB should avoid touching the water and protect pets, who can experience lethargy and loss of appetite if exposed to cyanobacteria, according to the Lake Hopatcong Foundation. Residents can report the bloom using an online form or by calling the NJDEP hotline at 1-877-WARNDEP (927-6337).