LIBERTY TOWNSHIP, N.J. (Warren County) — Mountain Lake remains under an Advisory Level water quality status after the New Jersey Department of Environmental Protection (NJDEP) detected elevated toxin concentrations despite declining algae levels, according to the Mountain Lake Community Association (MLCA).
The latest test results, posted by NJDEP following sampling on June 18 and June 23, show mixed indicators for the lake’s water quality. While cyanobacteria (blue-green algae) cell counts are below the advisory threshold, toxins released by the algae remain above safe levels.
-
June 18 results:
- Cyanobacteria cell count: 68,625 cells/mL (threshold: 80,000)
- Toxin concentration: 0.32 µg/L (threshold: 2.0 µg/L)
-
June 23 results:
- Cyanobacteria cell count: 32,875 cells/mL (well below threshold)
- Toxin concentration: 4.88 µg/L (more than double the threshold)
As a result, the public beach remains closed, and while swimming elsewhere in the lake is not prohibited, it is not advised. The MLCA is also urging residents not to consume lake water or fish caught in the lake, and to keep pets from drinking the water.
Despite the toxin spike, the MLCA reports that other water quality indicators are improving. On June 24, fluorometer readings — which track phycocyanin, a pigment used to detect cyanobacteria — were at their lowest levels of the season. In addition, water clarity was measured at 4.5 feet, and a stable thermocline (a natural water temperature boundary) was recorded at about 18 feet.
“We wish we knew why the toxin level surged back up on Monday after dropping last week,” MLCA said in a statement. “Perhaps we’re seeing the last gasps of the bloom. Toxins are often released when cyanobacteria die.”
Toxin levels can only be confirmed through lab testing, which NJDEP conducts. The agency plans to resample next week.
The MLCA said it remains committed to monitoring water quality conditions and communicating updates with the community. The organization also encouraged residents who are not yet members to consider joining to support ongoing efforts to prevent future algae blooms.
