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Posted Wednesday, July 3rd, 2019


The Department of Environmental Protection’s swimming and bodily contact advisory remains in effect for Lake Hopatcong due to a Harmful Algal Bloom, or HAB.

Photo of Lake Hopatcong shows algal bloom

Photo of Lake Hopatcong shows algal bloom

DEP sampling indicates that cell counts for cyanobacteria causing the bloom remain above the New Jersey Health Advisory Guidance levels. Consequently, the DEP advises continued closure of public swimming beaches and recommends the public avoid bodily contact with lake water.

This means swimming and watersports such jet-skiing, water-skiing, paddle-boarding, canoeing or kayaking should be avoided. There is no suggested limitation on more passive boating that does not involve bodily contact with lake water.

In addition to analyzing water sampling collected from areas throughout the lake on July 1 and 2, the DEP conducted aerial surveillance today. While interior, open portions of the lake appeared to be clearer than last week, water sampling showed continued elevated levels of cyanobacteria, with the highest levels below the surface.

This means that the water may appear free of a surface bloom, but dangerous bacteria can still be present below the surface.

photo shows a motor boat on Lake Hopatcong

Boating is allowed on Lake Hopatcong but DEP advisory cautions against recreational sports, such as water skiing, and direct contact with the water

Exposure to a harmful algal bloom can cause a range of health effects, including rashes, allergy-like reactions, flu-like symptoms, gastroenteritis, respiratory irritation and eye irritation. Exposure to a harmful algal bloom that is actively producing cyanotoxins may result in more serious health effects, including liver toxicity and neurological effects.

DEP’s sampling has not indicated the presence of toxins that can cause these more serious health effects. However, harmful algal blooms may begin producing cyanotoxins at any time. Consequently, DEP’s advisory against bodily contact with lake water will remain in place until conditions improve.

Cyanobacteria are naturally present in lakes and streams in low numbers. Under suitable environmental conditions – sunlight, high nutrients, warm temperatures and calm water – dense cyanobacterial blooms can form.

HABs, also known as blue-green algae. are usually a bright green, but can also appear as spilled paint, “pea soup,” or as having a thick coating or “mat” on the surface.

The first reports of isolated Harmful Algal Blooms were received by the DEP on June 17. The DEP increased monitoring and surveillance efforts in the lake last week after receiving more than 30 reports of Harmful Algal Blooms on the lake, including reports of people experiencing mild skin rashes after coming in contact with lake water.

Since last week, DEP has been conducting extensive water sampling throughout the lake, supplemented by aerial surveillance using special sensors that can estimate cyanobacteria cell counts. These efforts will continue.Lake Hopatcong: DEP Swimming Advisory Remains in Effect -- But Boating Allowed

In recent years, the DEP and the New Jersey Department of Health have been enhancing Harmful Algal Bloom surveillance and response efforts across the state.

In 2017, the DEP launched a campaign to educate the public about these blooms and provide resources on how to report them to the DEP. The “Avoid It and Report It” campaign advises the public to take the following steps when a suspicious bloom is observed:

  • Avoid contact with water in the vicinity of the bloom, especially in areas where the bloom is dense and forms scum;
  • Do not drink or consume the water;
  • Do not eat fish from the waterbody;
  • Keep pets and livestock away from the water;
  • Do not allow animals to drink the water, eat dried algae, or groom themselves after coming into contact with the water;
  • People, pets and livestock that come into contact with a bloom should rinse off with fresh water as soon as possible;
  • Seek medical attention or a veterinarian if a person or animal is experiencing adverse health effects after exposure to a bloom;
  • Report a suspected HAB by calling the DEP Hotline at 1-877-WARNDEP (877-927-6337), send a mobile alert through the WARN NJDEP mobile app (available via iTunes, Google Play or Windows Phone), or report via the DEP’s HAB website at