A losing battle?

“We’ve lost the north arm of the lake,” Eric Hastings told fellow members of the Greenwood Lake Commission at their meeting June 17.

A massive mat of water chestnuts is covering that section of the seven-mile-long lake, which is partly in New York and partly in New Jersey. The commission is working on remediation.

Interactive map above shows north end of Greenwood Lake’s east arm that is infested with water chestnuts. (Map by Megan Bowen)

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“We are beyond the point of protecting the lake,” said Jim Martin, another member of the bi-state commission formed in 2001 to improve the lake’s water quality.

Requiring that boats be power-washed before they are brought into the lake works before a chestnut incursion, but now Greenwood Lake poses a danger to other lakes, and boats need to be cleaned before they spread the chestnuts to those bodies of water, Martin said.

The milder winters in northern New Jersey and the Hudson Valley of New York state have allowed many new and unwelcome species to appear.

Water chestnuts are just one, but they are ubiquitous from the Hudson Valley to Quebec, he said.

European water chestnuts, Trapi natans, are different from Chinese water chestnuts, Eluocharis dulci, which are popular on Asian menus. They are native to Europe and also parts of Asia and Africa.

According to U.S. Department of Agriculture’s National Invasive Species Information Center, invasive water chestnuts form dense mats that displace native species.

Greenwood Lake has seen a serious water chestnut incursion for a couple of years, said Tom Howley, mayor of the Orange County, N.Y., village that shares the name of the lake.

Martin organized water scouts to pull the chestnuts out by hand June 7. About 50 people showed up, including about 20 with kayaks or boats.

They filled 120 laundry baskets with about 100 chestnuts each and those filled a dump truck.

While that barely made a dent in the problem, Martin hopes the effort enhanced awareness.

Fred Lubnow of Princeton Hydro, a consulting firm hired by most of the lake communities in northern New Jersey, said the unusually mild winters of the past few years were more likely precursors of a water chestnut problem.

Last winter was closer to normal but it didn’t keep the invasive plants away.

Pulling out plants

This was the first time in years that hand-pulling was used on Greenwood Lake.

An annual hand-pulling program exists on Lake Hopatcong, said Donna Macalle-Holly of the Lake Hopatcong Foundation.

She said the Knee Deep Club, a fisherman’s organization very active at the lake, initiated the water scout program, then the foundation took it over.

Hand-pulling is essential to make sure the entire rhizome is pulled out of the water, she said.

In a press release she prepared for the foundation newsletter, she noted that there are 22 designated scouting areas on the 2,500-acre lake.

The water chestnut problem has become less severe, with 23 plants pulled from the Woodport area of the lake in 2024, down from 78 the year before.

Macalle-Holly explained that the plants should be removed early in the season before hard seeds form and drop to the lakebed.

“We keep them in check because of rapid response,” she said.

Unfortunately, Greenwood Lake was not able to do that.

Adding dredging

Hastings said the commission would need to add dredging to its three-step program for ameliorating chestnuts: herbicides, hand-pulling and hydro raking.

The once-every-four-year drawdown is scheduled soon and will allow for dry dredging, which Martin called more effective than dredging through the water.

Although water chestnuts are the most critical problem on Greenwood Lake, they are not the only invasive species.

North of Fox Island in Greenwood Lake, there is evidence of a harmful algal bloom, or HAB.

Jack Roe, a commission member, speculated that the small area might be affected by a change in the pH, which measures acidity of the water, because of runoff from the Jennings Creek wildfire in November. The fire burned to the water’s edge.

He said that south of the island, the water is clear, indicating that something created a concentrated problem.

Often mistaken for algae, HABs are cyanotoxins, bacteria that can cause illness in humans, especially those who are particularly sensitive, and can be fatal to canines.

In 2019, an unexpected algal bloom in a small lake in Mebane, N.C., killed three family dogs before residents realized that cyanotoxins were present.

Cyanotoxins used to appear only late in the summer and rarely for long periods of time. But as the climate changes, the lakes warm earlier, allowing them to form.

Lake Hopatcong had a major problem with HABs in the summer of 2019. Beaches were closed and marinas suffered financial stress for a large portion of the season.

Pilot programs

HABs are treated in a number of ways. Phoslock was a standard treatment for early algal blooms, but it contains lanthanum, a soft, silvery-white metal known for its reactivity with both air and water. The metal binds with phosphorus, which is a major contributor to the growth of algal blooms.

The goal of lessening algal blooms is reached, but another chemical goes into the water.

Lubnow said the Army Corps of Engineers is working with Lake Hopatcong on two pilot programs to combat HABs.

Because the algal blooms primarily occur in shallow areas, the test programs are being run in Crescent Cove in Hopatcong and Ashley Cove in Jefferson.

In Crescent Cove, they are trying an oxygen-based treatment and in Ashley Cove, a more conventional algicide with kelated copper.

Lubnow would prefer using no chemicals in the lake and advocates for clay-based treatments that drag the toxins to the bottom of the lake. On the eastern end of the lake, the pilot program is combining some algicide with clay-based treatments.

“The copper-based treatments are effective and cheap but have an environmental impact,” he said.

The Army Corps of Engineers is funding the project and will do a cost-benefit analysis at the end of the season. It hopes to find an effective treatment for lakes all over the country, Lubnow said.

He said Lake Mohawk in Sparta has been monitored for cyanotoxins since the early 1990s but has not signed up this year.

The lake is private and a part of the New Jersey Coalition of Lake Associations along with other Sussex County lakes, including Lake Lenape, Swartzwood Lake, Kemah Lake, Hampton Lake and Lake Kittatinny. The association has used a lanthanum treatment when necessary for HABs.

Sabina Watson, a Lake Mohawk engineer, said the lake is looking good so far this season. “Cooler weather helps,” she noted.

Some green algae is present, which is not as serious as HABs, but the lake is aerated constantly to help increase the dissolved oxygen in both the upper and main lakes.

Harvesting weeds

Ironically, when the lakes suffer from HABs, which form on top of the water, sunlight doesn’t penetrate as well and the weeds aren’t as much of a problem.

“But at least we can harvest weeds,” Lubnow said.

Harvesting, which is regulated by the state Department of Environmental Protection, has helped control weeds in Lake Mohawk but is not planned this year, Watson said.

Lake Hopatcong received four harvesters and barges as well as operational funding from the state in the early 2000s. The state managed the harvesting program until a fatal accident threw the entire operation into chaos in June 2020. After the state pulled out, the Lake Hopatcong Commission took over the harvesting program.

Greenwood Lake also harvests weeds. The Village of Warwick holds the title to a harvester, but it is used by the commission in both states, Martin said.

According to the lake website, harvesters are out six to eight weeks each season. The lake also is drawn down every four years for stump removal and other maintenance.

Harvesting took off when New Jersey pulled back from chemical weed control early in the administration of former Gov. Chris Christie. Christie found funding for the Lake Hopatcong harvesters.

Harvesting not only keeps chemicals out of the lake, it pulls the weeds completely out of the water, Lubnow said.

If the weeds are allowed to die in the lake, they fall to the bottom, and as they decompose, they produce fertilizer for the next year’s weed growth. Harvesting pulls the weeds out by the roots. They are dumped into a barge and taken to a drying area. Once dried, they can be disposed of at a much lower cost than if they remained wet.

Shallow sections of the lakes cannot accommodate even a small harvester and are prone to weeds because sunlight reaches the lake bed.

Lake Mohawk is looking at a dredging project, said Watson, who has been educating residents about the importance of dredging.

Landing Channel, a manmade and very shallow section of Lake Hopatcong, also is set for eventual dredging.

In shallow areas, aeration can help control weeds, especially in areas where the predominant weed is European Water Milfoil, which does not have a strong root system. Martin said milfoil and curley pond weed are perennial problems in Greenwood Lake.

Limiting phosphorus

Keeping phosphorus out of the lakes is the best prevention because it is a great fertilizer of weeds. The lakes employ several means of capturing phosphorus, but education is the best defense, according to Lubnow and the Lake Hopatcong Commission.

Sanitary sewers finally will be installed around Lake Hopatcong after years of local officials struggling to find funding. Most of the land along Greenwood Lake does not have sewers.

Jefferson and Mount Arlington use a machine to clean road salt and other harmful chemicals from the storm sewer system. The foundation and commission both work to educate lakefront homeowners to avoid lawn treatments that can wash into the lake and encourage weed growth.

Martin said he is in favor of instructing property owners to put a buffer between their lawns and the lake. He said joking that poison ivy grows very well and also keeps trespassers away.

Geese, however, are immune from education efforts and contribute greatly to fertilizing weeds in all of the area lakes.

Other lakes in the New Jersey coalition are being monitored, Lubnow said.

Culver Lake in Frankford, the headwaters of the west branch of the Paulins Kill, which has a private lake association, is looking good, he said, but one area needs to be monitored every year.

Swartzwood Lake is “looking a little green,” according to several Stillwater residents. Swartzwood has a state grant for remediation and has used harvesting in the past.