Bacteria levels from a harmful algae bloom at Greenwood Lake are as much as 10 times higher than the state health standard, test results show.

Water samples taken Monday from the New Jersey side of the lake show cyanobacteria levels at 212,000 cells per milliliter, significantly more than the safe threshold of 20,000 cells per milliliter, according to lab results posted by the state Department of Environmental Protection.

That was the highest reading recorded from water samples taken at four sites that has prompted an advisory against swimming or any contact with the water at the lake, which spans 9 miles from Passaic County into Orange County, New York.

The other results were still well above the state standard, at 61,000 in the northern section of the New Jersey side of the lake, 90,000 in a middle section and 148,000 cells per milliliter at Browns Point, a park on the lake in West Milford.

The lab results show that bacteria levels rose this week from samples taken July 10. In one case the numbers doubled.

The highest reading at Lake Hopatcong — another major recreational lake under siege by an algae bloom — was 179,000 cells per milliliter taken on June 27 from Mount Arlington Beach.

On a conference call with reporters Thursday morning, DEP officials said that while the high cell count is concerning, it is hard to compare whether one outbreak is worse than another.

"The numbers are going to rise and fall throughout the event," said Robert Newby, a DEP microbiologist.

DEP officials said they suspect a combination of heavy rainfall, rising temperatures and climate change contributed to some of North Jersey's largest lakes being overwhelmed with algae, but said there is no definitive answer as to why it's happening this summer.

Several lakes in other Northeast states, including New York and Pennsylvania, are being inundated with algae blooms, said Bruce Friedman, the DEP's director of water monitoring standards.

And there is little that can be done except waiting for the algae to dissipate, Friedman said. "At this point, we're taking a monitoring approach," he said.

Aerial surveys confirmed the "extensive presence" of toxic algae throughout the southern New Jersey section of Greenwood Lake on Wednesday, a day after water samples prompted the closing of beaches and a public advisory to avoid contact with the water.

DEP officials said they don't know when the lake will be safe for swimming, wading, water sports and other recreational activities. A similar algae bloom at nearby Lake Hopatcong began in June and is entering its fourth week.

DEP officials called for closing all beaches on the New Jersey side of Greenwood Lake.

Boating and fishing are still allowed, but the DEP warns against eating any fish caught from the lake.

DEP scientists flying in a plane above Greenwood Lake on Wednesday were able to estimate levels of phycocyanin, a pigment present in cyanobacteria. They were correlated with water samples taken at the lake.

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Toxic cyanobacteria in the algae can cause skin irritation, stomach cramps, vomiting, nausea, diarrhea, fever, sore throat, headache, muscle and joint pain, blisters of the mouth and liver damage.

Paul Zarrillo, New Jersey chairman of the Greenwood Lake Commission, said there was a lot of misinformation online about the lake's condition, including one website that said the lake was completely closed.

"Just don't come into contact with the water. It's that simple," said Zarrillo, who lives on the lake.

The primary sources for the algae bloom are septic systems and fertilizer runoff.

This summer's weather patterns have created the perfect environment for algae to thrive, experts say. Intense but short rainstorms cause runoff into the lake; if several hot, sun-filled days follow, the blooms can spread extensively in still water.

The algae are usually a bright green. They can appear as splotches resembling spilled paint or as a thick coating on the surface. They may also be present in the water column below the surface.

In addition to the DEP samples, a team from Montclair State University will take water samples from 17 locations in Greenwood Lake in both New Jersey and New York on Friday. The work is being commissioned by the Greenwood Lake Commission, the bi-state agency that oversees the lake.

"It hopefully will give us a better picture of what we're dealing with and how extensive it is," Zarrillo said.