NJ Harmful algae blooms
Typical pea-soup appearance of harmful algae bloom. PHOTO CREDIT NJDEP

Manmade floating wetlands battle harmful algae bloom

| January 25, 2022

PENNINGTON – Harmful algal blooms plagued New Jersey freshwater lakes during the summer of 2019 and are a continuing concern whether the lake is Rosedale in Mercer County; Deal, the largest coastal lake, or Hopatcong, the largest in the state.

A combination of factors contributed to the 2019 blooms, Dr. Jason E. Adolf of the Monmouth University Urban Coast Institute and Department of Biology, explained at the Watershed Institute’s annual conference recently. 

Adolf explained that heavy June rains followed by unseasonably hot weather caused the early-season blooms to compromise swimming areas in many popular lakes during that particular summer.

Although called algal blooms, the growth is actually a bacteria caused by too much phosphorous in the water. The problem comes when the bacteria release a cyanotoxin that can cause illness, especially in pets, but also in people. 

Some people are sensitive to the cyanobacteria when the toxins aren’t present, Adolf said, and may end up with a skin rash.

When rain continues, it flushes the cyanotoxins out of the body of water promptly but continued dry, hot weather and still water keeps them in place.

There are a number of ways to detect blooms: Adolf explained that the most effective method is to use buoys to continuously record water conditions. Another is to have people take water samples in areas of high risk. 

A study of monitoring in Lake Hopatcong and the Manasquan Reservoir determined continuous data is better for forecasting than “grab” data. However, “citizen scientists” can provide useful data, which the state Department of Environmental Protection collects on a website. 


Monitoring is important, but keeping phosphorous out of the water is the goal. One method being tried is the construction of floating wetland islands, which are being installed in Rosedale Lake. 

Steve Tuorto, director of science and stewardship at the Watershed Institute, described that project as an excellent way to control phosphorous. 

Floating wetland islands consist of a buoyant material planted with vegetation that drops roots deep into the water, producing a substantial surface area to catch algal biomass and keep it from the water. Creating a proper artificial wetland can produce a mat surface area equivalent to nearly 175 times that of a natural wetland. 

The buoyant material is 100 percent recycled, mostly from water bottles. There are five layers and the islands are placed where there is plenty of room for the roots. The top layer is two inches deep and dense enough that it won’t break down. Foam on the bottom allows for extra buoyancy. 

The islands are not invulnerable, however. Goose netting is necessary or the birds will eat the vegetation. Swans and ducks pose some danger, but geese are the major problem, Tuorto said. Turtles enjoy the islands without doing any damage, he added.

The wetland islands in Lake Hopatcong will be placed in two of the shallower sections, Landing Channel in Roxbury Township and Ashley Cove in Jefferson Township. Many other techniques are used on the deeper sections of that lake, including aeration, biochar, which captures the phosphorous, and stream bank stabilization, which keeps phosphorous out of the water.

Jane Primerano

Jane Primerano

Jane Primerano has covered agriculture and environmental issues in the Northeast for nearly a decade after 20+ years of reporting on municipal and county government, police and education for weekly and daily newspapers in New Jersey and Pennsylvania.

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