LIBERTY TOWNSHIP, N.J. (Warren County) — A prolonged harmful algal bloom in Mountain Lake is showing no signs of abating, with the latest test results from the New Jersey Department of Environmental Protection confirming elevated cell counts and toxin levels, according to the Mountain Lake Community Association (MLCA).
On Wednesday, May 28, NJDEP collected water samples at the lake’s boat ramp and adjacent swimming beach. Lab results released Friday showed cyanobacteria cell counts of 80,750 cells/mL and 82,250 cells/mL, respectively. Toxin levels measured 4.79 µg/L at the boat ramp and 3.58 µg/L at the beach. Both sites remain above the advisory threshold of 80,000 cells/mL and 2.0 µg/L of toxin.
The data, now published on NJDEP’s Harmful Algal Bloom (HAB) Dashboard, indicate that the bloom is intensifying. Previous testing on April 22 showed cell counts of 62,875 cells/mL and toxin levels of 2.43 µg/L. Samples from April 2 measured lower cell counts but showed higher toxins at 8.02 µg/L.
Under the ongoing advisory status — indicated by orange signs posted around the lake — residents and visitors are urged to avoid swimming and any activities involving direct contact with lake water. Pets should be kept away from the water, and fish caught in the lake should not be consumed.
The MLCA’s own monitoring, conducted Tuesday, May 27, supports the DEP’s findings. Water clarity was reported at just 2.5 feet, with elevated algae meter readings. Surface temperature, oxygen, and pH levels remain within expected ranges, and a thermocline is forming at about 18 feet — typical for late May.
Phosphorus samples have been collected at multiple depths and submitted for analysis, the MLCA said. Results will be shared once available.
The association acknowledged widespread disappointment with this year’s poor water quality and noted that prolonged rainfall likely contributed to nutrient-rich runoff entering the lake — a key driver of blue-green algae blooms. While some nutrient input is natural, officials emphasized the need to reduce preventable sources, such as fertilizers and failing septic systems.
“Everyone living in the Mountain Lake watershed needs to do everything possible to prevent nutrients from entering the lake,” the MLCA said in a statement.
With additional rainfall in the forecast, officials say water quality improvements are unlikely in the short term. Monitoring efforts will continue, and updates will be provided as new data becomes available.
