South Lake
Herkimer County, New York499 acresView mapDirections
NY DEC publishes the water-quality measurements for South Lake. Here is what has been measured.
- Oligotrophic
- 38 ft max depth
South Lake in Herkimer County, New York has water-quality measurements published by NY DEC, shown here as reported. Phosphorus: 4 µg/L. Chlorophyll-a (algae): 1.1 µg/L. Surface area: 499 acres.
South Lake is a 499-acre cold, clear oligotrophic lake in Herkimer County, New York with an estimated average depth of about 38 feet. Overall water quality is improving over recent sampling years. Compared to the 5 other monitored lakes in Herkimer County, South Lake ranks #1 for water quality.
Source: EPA Water Quality Portal sampling records, NYSDEC, last sampled 2023-09-06. 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. Check local advisories before you swim.
Whether South Lake is safe to swim in today is a call for the New York Department of Environmental Conservation and the county health department, who post current advisories. LakeQuality does not issue swimming clearances.
Water quality measurements for South Lake
These are the measurements NY DEC publishes for South Lake, shown as reported. The condition class beside each reading is the EPA National Lakes Assessment class for this lake’s ecoregion.
No clarity data. Phosphorus 4 µg/L. Chlorophyll-a 1.1 µg/L. TSI 28.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | No reading How deep a black-and-white disk stays visible from the surface. Higher is clearer. | |
| Total phosphorus | 4µg/L | Good GoodFairPoor |
| Chlorophyll-a (algae) | 1.1µg/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. | 28 | Oligotrophic OligotrophicMesotrophicEutrophicHypereutrophic |
Low nutrients, clear water. No reading is a swimming clearance.
Ask about South Lake
Answers come straight from the public measurements and survey records on this page.
Water Temperature
South Lake typically sits around 67°F at the surface in September. Summer average is about 73°F. Usually warmest in Jul (about 73°F) and coldest in Feb (about 33°F). These are typical values by month — not a live reading.
Column height runs from this lake’s coldest month (33°F) to its warmest (73°F).
Typical surface water temperature by month, from 32 field readings (2017–2022) via the EPA Water Quality Portal. See the full South Lake water temperature breakdown →
Lake Details
Max depth
~38 ft est.
Surface area
499 acres
Depth marked “est.” is a modeled maximum from GLOBathy (Khazaei et al. 2022, CC0), not a measured survey. New York has not published bathymetry for South Lake.
Lake Size & Watershed
Watershed (drainage) area
12 sq mi
HydroLAKES / HydroSHEDS
Shoreline
6.7 mi
HydroLAKES / HydroSHEDS
Elevation
2,028 ft
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS). Mean depth here is modelled, not surveyed — HydroLAKES v1.0 estimates lake depth from surrounding terrain rather than from soundings. Treat it as an approximation, and prefer a state bathymetric survey where one exists.
Stays via Stay22
Stays near South Lake
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Fishing South Lake
Water Quality Trend: Improving
Based on 4 years of monitoring (2020–2023).
Phosphorus
Improving-12.05 µg/L/yr4 years
Chlorophyll-a
Improving-0.05 µg/L/yr3 years
Reservoir Info (USACE NID)
South Lake is a man-made reservoir impounded by the South Lake Dam (completed 1901), built primarily for recreation on the SOUTH BRANCH BLACK RIVER; earth-type dam, 30 ft tall and 380 ft long.
- Surface area
- 499 ac
- Normal storage
- 4,840 ac-ft
- Max storage
- 5,480 ac-ft
- Hazard class
- High
- Owner
- New York State Canal Corporation
Source: USACE National Inventory of Dams, NID ID NY00317 · Operator website
Nearby Lakes in Herkimer County
Frequently asked questions about South Lake
Where is South Lake?
- South Lake is a lake in Herkimer County, New York. Its water-quality measurements are published by NY DEC and shown on this page as reported.
What is the water quality of South Lake?
- South Lake in Herkimer County, New York has water-quality measurements published by NY DEC, shown here as reported. Phosphorus: 4 µg/L. Chlorophyll-a (algae): 1.1 µg/L. Surface area: 499 acres.
Is South Lake safe to swim in?
- Nutrient and algae readings are not a swimming clearance. Check local advisories before you swim.
What is the water temperature of South Lake?
- South Lake typically sits around 67°F at the surface in September, from 32 EPA Water Quality Portal field readings (2017–2022). That is a typical value for the month, not a live reading.
How deep is South Lake?
- No published bathymetric survey covers South Lake, so its depth has not been measured. The HydroLAKES global model estimates an average depth of about 38 feet, but that is a modelled estimate derived from surrounding terrain rather than a measurement on the water, so treat it as approximate. The lake covers 499 acres.
Explore South Lake across LakeQuality
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Where this data comes from
39 measurements from 1 monitoring station, 2020–2023. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- USGS New York Water Science Center
USGS-NY39 samples · 2020–2023
Analytical methods
- P, wu, WCA, persulfate CF color
- Chlorophyll a,fluorometric,uncor
Monitoring station identifiers (1)
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
Lake size & watershed from HydroLAKES (HydroSHEDS)