South Lake
Herkimer County, New York499 acresView mapDirections
Clarity, phosphorus, and algae all sit in the cleanest band for this region.
- Oligotrophic
- #1 of 6 in the county
- 38 ft max depth
South Lake in Herkimer County, New York has a water quality grade of A (Excellent). Phosphorus: 4 µg/L. Chlorophyll-a (algae): 1.1 µg/L. Surface area: 499 acres.
- Typical in September
- 67°F
- Max depth
- ~38 ft est.
- Area
- 499 acres
- Type
- Oligotrophic
- Phosphorus
- 4 µg/L
- Chlorophyll-a
- 1.1 µg/L
- Trend
- ↑ Improving
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Watch South Lake’s letter
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South Lake is a 499-acre cold, clear oligotrophic lake in Herkimer County, New York with an estimated average depth of about 38 feet. Water quality is graded A based on 2 sampling years through 2023. 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. Grade methodology: LakeQuality methodology.
Swimming Safety
Grade onlyLow algae
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.
The A is nutrients and algae, not a swimming clearance. Check local advisories before you swim.
Water Quality Grade: A (Excellent)
No clarity data. Phosphorus 4 µg/L. Chlorophyll-a 1.1 µg/L. TSI 28. The letter is not a swimming clearance.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | No recent samples | |
| Phosphorus | 4 µg/L | Good |
| Chlorophyll-a (Algae) | 1.1 µg/L | Good |
| Trophic State Index (TSI) | 28 | Oligotrophic |
Low nutrients, clear water. The letter is not a swimming clearance.
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.
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
| Characteristic | Value |
|---|---|
| Maximum Depth | ~38 ft est. |
| Average Depth | ~32 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
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.
Fishing South Lake
Water Quality Trend: ↑ Improving
Based on 4 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Phosphorus | ↑ Improving | -12.05 µg/L/yr | 4 |
| Chlorophyll-a | ↑ Improving | -0.05 µg/L/yr | 3 |
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
County Ranking
Ranked #1 of 6 lakes in Herkimer County
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. LakeQuality grades it A for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for South Lake?
- South Lake in Herkimer County, New York has a water quality grade of A (Excellent). Phosphorus: 4 µg/L. Chlorophyll-a (algae): 1.1 µg/L. Surface area: 499 acres.
Is South Lake safe to swim in?
- The A is nutrients and algae, 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
Depth, room, public access, and the state wake-sport rules
Species activity outlook by water temperature and season
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Where to stay at New York's top lakes, each with its grade
Low nutrients, clear water. The letter is not a swimming clearance.
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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)
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
Lake size & watershed from HydroLAKES (HydroSHEDS)