Gropp Lake
Gropp Lake in Mercer County, New Jersey has a water quality grade of C (Fair). Water clarity: 3.3 ft visibility. Phosphorus: 35 µg/L. Chlorophyll-a (algae): 25.8 µg/L. Surface area: 41 acres.
- Clarity
- 3.3 ft
- Area
- 41 acres
- Type
- Eutrophic
- Public access
- Yes
Gropp Lake is a 41-acre productive, nutrient-rich eutrophic lake in Mercer County, New Jersey. Water quality is graded C based on 2 sampling years through 2024. Limited fish-species data available. Public access is available with 1 public boat landing. Compared to the 14 other monitored lakes in Mercer County, Gropp Lake ranks #2 for water quality.
Source: EPA Water Quality Portal sampling records, your state environmental agency, last sampled 2024-11-14. Grade methodology: LakeGrade methodology.
Watch Gropp Lake water quality
Subscribe for LakeQuality updates by email. No spam, unsubscribe anytime.
Swimming Safety
Grade onlyBacteria advisory
Based on clarity and algae grades from past sampling — we do not hold live water temperature and a current cyanobacteria reading for this lake. Check your state or county health department before you swim.
Swim with caution, moderate algae may be present
Water Quality Grade: C (Fair)
Very murky, less than 3.3 ft of visibility. Phosphorus level: 35 µg/L. Chlorophyll-a: 25.8 µg/L. Trophic State Index: 59.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 3.3 ft | Not graded |
| Phosphorus | 35 µg/L | Good |
| Chlorophyll-a (Algae) | 25.8 µg/L | Fair |
| Trophic State Index (TSI) | 59 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Where to stay near Gropp Lake
Compare lakeside cabins, hotels, and vacation rentals near Gropp Lake in Mercer County, New Jersey — live availability and prices for your trip. Switch the map to Satellite to see the lake and how close each stay is to the water.
Top-rated places to stay near Gropp Lake
Availability and prices from Stay22 partners (Booking.com, Vrbo, Expedia). We may earn a commission from bookings, at no extra cost to you.
Lake Details
| Characteristic | Value |
|---|---|
| Surface Area | 41 acres |
| Public Access | Yes |
No bathymetric survey has been published for Gropp Lake, so its depth is not documented here.
Recreation & Access
- Ross Marine Service, TrentonPublic
Named access points from the USGS National Boat Ramps inventory, snapped within 5 km. More lakes with boat ramps
Fishing Gropp Lake
Reservoir Info (USACE NID)
Gropp Lake is a man-made reservoir impounded by the Gropps Lake Dam (completed 1900), built primarily for recreation on the Back Creek; earth-type dam, 25 ft tall and 485 ft long.
- Surface area
- 41 ac
- Normal storage
- 211 ac-ft
- Max storage
- 549 ac-ft
- Drainage area
- 7.9 sq mi
- Hazard class
- Low
- Owner
- Township of Hamilton
Source: USACE National Inventory of Dams, NID ID NJ00235 · Operator website · Matched by proximity (0.53 km)
EPA Impairment Status
Gropp Lake is officially listed as impaired under Clean Water Act §303(d) in the 2022 EPA reporting cycle (IR category 5).
Causes of impairment
Source: EPA ATTAINS assessment unit NJ02040201070020-01 · Official waterbody report · Matched by proximity (1.88 km)
County Ranking
Ranked #2 of 15 lakes in Mercer County
Nearby Lakes in Mercer County
Frequently asked questions about Gropp Lake
Where is Gropp Lake?
- Gropp Lake is a lake in Mercer County, New Jersey. LakeQuality grades it C for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Gropp Lake?
- Gropp Lake in Mercer County, New Jersey has a water quality grade of C (Fair). Water clarity: 3.3 ft visibility. Phosphorus: 35 µg/L. Chlorophyll-a (algae): 25.8 µg/L. Surface area: 41 acres.
Is Gropp Lake safe to swim in?
- Swim with caution, moderate algae may be present. Gropp Lake has a water quality grade of C (Fair). Algae concentration (chlorophyll-a) is 25.8 µg/L. Always check local health department advisories before swimming.
Are there boat ramps on Gropp Lake?
- Gropp Lake has 1 documented boat landing in the USGS National Boat Ramps inventory. Named access points include Ross Marine Service, Trenton. Public access is listed as yes.
Explore Gropp Lake across LakeGrade
More New Jersey Lake Rankings
Other Grade C Lakes in New Jersey
Eutrophic Lakes in New Jersey
Where this data comes from
32 measurements from 2 monitoring stations, 2024. Retrieved from the EPA Water Quality Portal on 2026-08-21.
Collected and reported by
- NJDEP Bureau of Freshwater and Biological Monitoring
NJDEP_BFBM32 samples · 2024
Analytical methods
- Phosphorus by Colorimetry
- 445.0 ~ EPA; Chlorophyll and Pheophytin in Algae by Fluorescence
Monitoring station identifiers (2)
Grade thresholds from the EPA National Lakes Assessment (EPA 841-R-24-006, Table 6-3), applied by ecoregion. See how grades are calculated and data sources.
Other records on this page
Impairment status from EPA ATTAINS 303(d) database
Named boat-access points from the USGS National Boat Ramps inventory