Sweetwater Lake
Ramsey County, North DakotaView mapDirections
Clarity, phosphorus, and algae sit in the clean band for this region.
↑ up from D at the last regrade
- Eutrophic
- #1 of 8 in the county
- 50 ft max depth
- Limited data
Sweetwater Lake in Ramsey County, North Dakota has a water quality grade of B (Good). Water clarity: 3 ft visibility. Phosphorus: 655.5 µg/L. Chlorophyll-a (algae): 10.7 µg/L.
- Clarity
- 3 ft
- Typical in September
- 60°F
- Max depth
- ~50 ft est.
- Type
- Eutrophic
- Phosphorus
- 655.5 µg/L
- Chlorophyll-a
- 10.7 µg/L
- Trend
- → Stable
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Watch Sweetwater Lake’s letter
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Sweetwater Lake is a productive, nutrient-rich eutrophic lake in Ramsey County, North Dakota with an estimated average depth of about 50 feet. Water quality is graded B based on 1 sampling years through 2023. Phosphorus level is declining over recent sampling years. Compared to the 7 other monitored lakes in Ramsey County, Sweetwater Lake ranks #1 for water quality.
Source: EPA Water Quality Portal sampling records, NDDEQ, last sampled 2023-10-17. Grade methodology: LakeQuality methodology.
Swimming Safety
Grade onlyLimited data
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 B is nutrients and algae, not a swimming clearance. Check local advisories before you swim.
Water Quality Grade: B (Good)
Very murky, less than 3 ft of visibility. Phosphorus 655.5 µg/L. Chlorophyll-a 10.7 µg/L. TSI 71. The letter is not a swimming clearance.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 3 ft | Not graded |
| Phosphorus | 655.5 µg/L | Not graded |
| Chlorophyll-a (Algae) | 10.7 µg/L | Good |
| Trophic State Index (TSI) | 71 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Water Temperature
Sweetwater Lake typically sits around 60°F at the surface in September. Summer average is about 70°F. Usually warmest in Jul (about 73°F) and coldest in Feb (about 34°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 254 field readings (2010–2023) via the EPA Water Quality Portal. See the full Sweetwater Lake water temperature breakdown →
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | ~50 ft est. |
| Average Depth | ~8 ft est. |
Depth marked “est.” is a modeled maximum from GLOBathy (Khazaei et al. 2022, CC0), not a measured survey. North Dakota has not published bathymetry for Sweetwater 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 Sweetwater Lake
Water Quality Trend: → Stable
Based on 4 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | → Stable | +0.143 m/yr | 3 |
| Phosphorus | ↓ Declining | +187.79 µg/L/yr | 3 |
| Chlorophyll-a | ↑ Improving | -42.12 µg/L/yr | 4 |
County Ranking
Ranked #1 of 8 lakes in Ramsey County
Nearby Lakes in Ramsey County
Frequently asked questions about Sweetwater Lake
Where is Sweetwater Lake?
- Sweetwater Lake is a lake in Ramsey County, North Dakota. LakeQuality grades it B for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Sweetwater Lake?
- Sweetwater Lake in Ramsey County, North Dakota has a water quality grade of B (Good). Water clarity: 3 ft visibility. Phosphorus: 655.5 µg/L. Chlorophyll-a (algae): 10.7 µg/L.
Is Sweetwater Lake safe to swim in?
- The B is nutrients and algae, not a swimming clearance. Check local advisories before you swim.
What is the water temperature of Sweetwater Lake?
- Sweetwater Lake typically sits around 60°F at the surface in September, from 254 EPA Water Quality Portal field readings (2010–2023). That is a typical value for the month, not a live reading.
How deep is Sweetwater Lake?
- No published bathymetric survey covers Sweetwater Lake, so its depth has not been measured. The HydroLAKES global model estimates an average depth of about 50 feet, but that is a modelled estimate derived from surrounding terrain rather than a measurement on the water, so treat it as approximate.
Explore Sweetwater Lake across LakeQuality
Species activity outlook by water temperature and season
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Where to stay at North Dakota's top lakes, each with its grade
High nutrients, frequent algae, reduced clarity
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Where this data comes from
31 measurements from 1 monitoring station, 2020–2023. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- USGS North Dakota Water Science Center
USGS-ND31 samples · 2020–2023
Analytical methods
- P, wu, WCA, persulfate CF color
- Plant pigments, sonication & 445
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)
Depth, fish, and access data from North Dakota Game & Fish