New Jersey Lake Water Quality

New Jersey lists 343 lakes across 20 counties, 99 of them with a recent water-quality reading. Most of that sampling flows through monitoring run by the New Jersey Department of Environmental Protection, which feeds state, federal, and volunteer measurements into the EPA Water Quality Portal. The remainder are here because they are real named lakes, not because anyone has sampled them recently. The measured lakes spread across the range: low phosphorus and algae readings in the deeper basins, higher readings in the agricultural south of the state.

By surface area the largest lake here is Wanaque Reservoir, at about 1,971 acres, and 16 of the lakes in this index cover more than 500 acres. Size is worth knowing before you go: a large deep basin buffers nutrient inputs by sheer volume, while a shallow one warms quickly and can turn over its whole water column in a single summer storm. Eutrophic conditions dominate the measured set: nutrient-loaded, productive, with algal pressure that shows up most years in late summer. These lakes tend to be shallow, in agricultural watersheds, and over-warmed by the time July ends. Cape May has the lowest nutrient and algae readings on average. With only 20 counties in the state, the cross-county spread is narrower than the within-county spread for most lakes.