Lake Topanemus
Monmouth County, New Jersey22 acresView mapDirections
NJDEP publishes the water-quality measurements for Lake Topanemus. Here is what has been measured.
- Eutrophic
- Impaired · Impaired biota (cause unknown)
Lake Topanemus in Monmouth County, New Jersey has water-quality measurements published by NJDEP, shown here as reported. Water clarity: 5.4 ft visibility. Phosphorus: 24.9 µg/L. Chlorophyll-a (algae): 10.2 µg/L. Surface area: 22 acres.
Lake Topanemus is a 22-acre productive, nutrient-rich eutrophic lake in Monmouth County, New Jersey. Compared to the 3 other monitored lakes in Monmouth County, Lake Topanemus ranks #1 for water quality.
Source: EPA Water Quality Portal sampling records, your state environmental agency, last sampled 2023-11-02. Methodology: how these readings are compared.
Swimming conditions
Readings onlyLow algae
Based on clarity and algae readings from past sampling — there is no live water temperature and a current cyanobacteria reading for this lake. Check your state or county health department before you swim.
Nutrient and algae readings are not a swimming clearance. Lake Topanemus is listed impaired under Clean Water Act §303(d) (IR 5) for impaired biota (cause unknown), nutrients (phosphorus, nitrogen). Check local advisories before you swim.
Whether Lake Topanemus is safe to swim in today is a call for the New Jersey Department of Environmental Protection and the county health department, who post current advisories. LakeQuality does not issue swimming clearances.
Water quality measurements for Lake Topanemus
These are the measurements NJDEP publishes for Lake Topanemus, shown as reported. The condition class beside each reading is the EPA National Lakes Assessment class for this lake’s ecoregion.
Murky, only visible to about 5.4 ft. Phosphorus 24.9 µg/L. Chlorophyll-a 10.2 µg/L. TSI 52.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | 5.4ft | Measured, not scored How deep a black-and-white disk stays visible from the surface. Higher is clearer. |
| Total phosphorus | 24.9µg/L | Good GoodFairPoor |
| Chlorophyll-a (algae) | 10.2µg/L | Good GoodFairPoor |
| Trophic state (TSI)Carlson's 0–100 index of how much algae a lake can support, from clarity, phosphorus and chlorophyll-a. | 52 | Eutrophic OligotrophicMesotrophicEutrophicHypereutrophic |
High nutrients, frequent algae, reduced clarity
Ask about Lake Topanemus
Answers come straight from the public measurements and survey records on this page.
Lake Details
Surface area
22 acres
No bathymetric survey has been published for Lake Topanemus, so its depth is not documented here.
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Stays near Lake Topanemus
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Fishing Lake Topanemus
Reservoir Info (USACE NID)
Lake Topanemus is a man-made reservoir impounded by the Lake Topanemus Dam (completed 1915), built primarily for recreation on the McGellaird's Brook; earth-type dam, 20 ft tall and 327 ft long.
- Surface area
- 22 ac
- Normal storage
- 66 ac-ft
- Drainage area
- 1.6 sq mi
- Hazard class
- High
- Owner
- Monmouth County Engineering
Source: USACE National Inventory of Dams, NID ID NJ00219 · Operator website
EPA Impairment Status
Lake Topanemus is officially listed as impaired under Clean Water Act §303(d) in the 2022 EPA reporting cycle (IR category 5).
Causes of impairment
Designated uses not supporting: Aquatic life.
A Total Maximum Daily Load (TMDL) plan has been approved.
Source: EPA ATTAINS assessment unit NJ02030105150020-01 · Official waterbody report
Nearby Lakes in Monmouth County
Frequently asked questions about Lake Topanemus
Where is Lake Topanemus?
- Lake Topanemus is a lake in Monmouth County, New Jersey. Its water-quality measurements are published by NJDEP and shown on this page as reported.
What is the water quality of Lake Topanemus?
- Lake Topanemus in Monmouth County, New Jersey has water-quality measurements published by NJDEP, shown here as reported. Water clarity: 5.4 ft visibility. Phosphorus: 24.9 µg/L. Chlorophyll-a (algae): 10.2 µg/L. Surface area: 22 acres.
Is Lake Topanemus safe to swim in?
- Nutrient and algae readings are not a swimming clearance. Lake Topanemus is listed impaired under Clean Water Act §303(d) (IR 5) for impaired biota (cause unknown), nutrients (phosphorus, nitrogen). Check local advisories before you swim.
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Where this data comes from
72 measurements from 3 monitoring stations, 2022–2023. Retrieved from the EPA Water Quality Portal on 2026-08-21.
Collected and reported by
- NJDEP Bureau of Freshwater and Biological Monitoring
NJDEP_BFBM72 samples · 2022–2023
Analytical methods
- Phosphorus by Colorimetry
- 445.0 ~ EPA; Chlorophyll and Pheophytin in Algae by Fluorescence
Monitoring station identifiers (3)
EPA condition classes from the National Lakes Assessment (EPA 841-R-24-006, Table 6-3), applied by ecoregion. See where the data comes from and data sources.
Other records on this page
Impairment status from EPA ATTAINS 303(d) database