Mercer County Lake Quality
New Jersey, 5 lakes, average grade D (Nutrient-rich)
Mercer County has 5 graded lakes — a thin enough sample that one or two stressed lakes can move the county average noticeably. Use the per-lake pages below for what actually matters. The county-wide average grade is D — water quality issues are persistent across most of the monitored basins. 3 lakes fall into the F bracket outright.
Most of the county's monitored lakes are shallow — under 50 feet — which means wind keeps the water column mixed all summer and sediment-bound phosphorus releases back into the surface layer whenever the bottom is disturbed. Meadow Lakes (B) is the cleanest in the county.
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Quick Answers for Mercer County
Planning a trip? Check special fishing regulations for Meadow Lakes — or check the official New Jersey fishing regulations.
All Lakes in Mercer County
5 lakes5 graded lakes
| # | Lake | Grade | Clarity | Phosphorus | Algae | Trophic | Access |
|---|---|---|---|---|---|---|---|
| 1 | BMeadow LakesMercer | B | 4.3 ft | 26.9 µg/L | 7.6 µg/L | No recent samples | Not recorded |
| 2 | CGropp LakeMercer | C | 3.3 ft | 35 µg/L | 25.8 µg/L | No recent samples | Not recorded |
| 3 | FCarnegie LakeMercer | F | 2.1 ft | 110.5 µg/L | 40.8 µg/L | No recent samples | Not recorded |
| 4 | FCurlis LakeMercer | F | 2.4 ft | 121 µg/L | 49.8 µg/L | No recent samples | Not recorded |
| 5 | FEtra LakeMercer | F | 3.9 ft | 46.6 µg/L | 35.4 µg/L | No recent samples | Not recorded |
Lake Match
Which lake suits how you actually use one?
Six questions — swimming, fishing, quiet, cabins, drive time — and a shortlist of graded lakes that fit, with the water quality behind each one.
Other Counties in New Jersey
See how Mercer County stacks up in the national county water-quality rankings, or browse the full directory of graded lakes across all 49 states and 2 Canadian provinces.
Source: EPA National Aquatic Resource Surveys, 2026.