LIBERTY TOWNSHIP, N.J. (Warren County) — A harmful algal bloom advisory has been issued for Mountain Lake in Liberty Township, according to New Jersey Fish & Wildlife.
Officials warned that fish caught from the lake should not be consumed while the advisory remains in effect.
As a result, rainbow trout that were scheduled to be stocked at Mountain Lake this spring will instead be released into the Pequest River.
According to the Mountain Lake Community Association, the New Jersey Department of Environmental Protection collected a water sample March 17, four days after the lake’s ice melted, and testing showed an early-season cyanobacteria bloom.
The sample recorded 31,125 cells per milliliter, above the state’s 20,000 “watch” threshold but below the 80,000 “advisory” level. However, toxin levels measured 2.32 micrograms per liter, exceeding the state’s advisory threshold of 2.0 micrograms per liter, prompting the advisory designation.
Officials said the advisory means pets should not ingest lake water and fish from the lake should not be eaten.
Mountain Lake is one of only two lakes in New Jersey sampled by the Department of Environmental Protection so far this year. The lake was selected for follow-up testing after samples collected Dec. 1, 2025, showed a late-season bloom with cell counts ranging from 38,250 to 44,150 cells per milliliter and toxin levels between 7.80 and 10.23 micrograms per liter.
The association noted that early-season blooms are not uncommon during spring turnover. Previous April sampling showed varying cell counts, including 54,500 cells per milliliter in 2022, 161,732 in 2023, 11,877 in 2024 and 55,500 in 2025.
Cyanobacteria occur naturally at low levels and are typically not a concern. However, a harmful algal bloom, or HAB, refers to excessive growth of cyanobacteria, some of which can produce toxins that may be harmful to humans, pets, livestock and wildlife.
The Mountain Lake Community Association said it will continue monitoring conditions in coordination with the DEP and expects the bloom may subside as seasonal conditions stabilize, though weather and runoff can impact water quality.
Current conditions and updates can be found on the state’s HAB dashboard online.
