Simian Lake
Simian Lake in St. Louis County, Minnesota has a water quality grade of C (Fair). Water clarity: 3.9 ft visibility. Phosphorus: 33 µg/L. Chlorophyll-a (algae): 5.5 µg/L.
- Clarity
- 3.9 ft
- Typical in August
- 67°F
- Mean depth
- ~10 ft est.
- Type
- Eutrophic
- Trend
- ↓ Declining
- Public access
- No
Next lake in St. Louis County
Simian Lake is a productive, nutrient-rich eutrophic lake in St. Louis County, Minnesota with an estimated average depth of about 10 feet. Water quality is graded C based on 2 sampling years through 2024. Overall water quality is declining over recent sampling years. Limited fish-species data available. No public access — the lake is private or restricted. Compared to the 67 other monitored lakes in St. Louis County, Simian Lake ranks #53 for water quality.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2024-10-03. Grade methodology: LakeGrade methodology.
Watch Simian Lake water quality
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Swimming Safety
Grade onlyModerate
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.
Generally safe for swimming, moderate water quality
Water Quality Grade: C (Fair)
Murky, only visible to about 3.9 ft. Phosphorus level: 33 µg/L. Chlorophyll-a: 5.5 µg/L. Trophic State Index: 53.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 3.9 ft | Not graded |
| Phosphorus | 33 µg/L | Fair |
| Chlorophyll-a (Algae) | 5.5 µg/L | Good |
| Trophic State Index (TSI) | 53 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Where to stay near Simian Lake
Compare lakeside cabins, hotels, and vacation rentals near Simian Lake in St. Louis County, Minnesota — 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 Simian Lake
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Planning a whole trip? See where to stay at Minnesota’s top lakes →
Water Temperature
Simian Lake typically sits around 67°F at the surface in August. Summer average is about 66°F. Usually warmest in Aug (about 67°F) and coldest in May (about 52°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 126 field readings (2010–2021) via the EPA Water Quality Portal. See the full Simian Lake water temperature breakdown →
Lake Details
| Characteristic | Value |
|---|---|
| Average Depth | ~10 ft est. |
| Public Access | No |
Depth marked “est.” is a modeled estimate from HydroLAKES, not a measured survey. Minnesota has not published bathymetry for Simian 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 Simian Lake
Water Quality Trend: ↓ Declining
Based on 5 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↑ Improving | +0.276 m/yr | 5 |
| Phosphorus | ↓ Declining | +23.35 µg/L/yr | 4 |
| Chlorophyll-a | ↓ Declining | +1.02 µg/L/yr | 5 |
EPA Impairment Status
Simian Lake is officially listed as impaired under Clean Water Act §303(d) in the 2019 EPA reporting cycle.
Causes of impairment
Source: EPA ATTAINS assessment unit FDL_118 · Official waterbody report
County Ranking
Ranked #53 of 68 lakes in St. Louis County
Nearby Lakes With Higher Grades
Simian Lake holds Grade C. 3 nearby lakes hold higher nutrient-and-algae grades — useful for a swim day, not a reason to skip lodging here.
See full comparison →Nearby Lakes in St. Louis County
Frequently asked questions about Simian Lake
What is the water quality grade for Simian Lake?
- Simian Lake in St. Louis County, Minnesota has a water quality grade of C (Fair). Water clarity: 3.9 ft visibility. Phosphorus: 33 µg/L. Chlorophyll-a (algae): 5.5 µg/L.
Is Simian Lake safe to swim in?
- Generally safe for swimming, moderate water quality. Simian Lake has a water quality grade of C (Fair). Algae concentration (chlorophyll-a) is 5.5 µg/L. Always check local health department advisories before swimming.
What is the water temperature of Simian Lake?
- Simian Lake typically sits around 67°F at the surface in August, from 126 EPA Water Quality Portal field readings (2010–2021). That is a typical value for the month, not a live reading.
How deep is Simian Lake?
- No published bathymetric survey covers Simian Lake, so its depth has not been measured. The HydroLAKES global model estimates an average depth of about 10 feet, but that is a modelled estimate derived from surrounding terrain rather than a measurement on the water, so treat it as approximate.
Explore Simian Lake across LakeGrade
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Where this data comes from
203 measurements from 1 monitoring station, 2020–2024. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Fond du Lac Band of Chippewa (MN)
FONDULAC_WQX203 samples · 2020–2024
Analytical methods
- Phosphorus by Two Reagent Colorimetry
- Phosphorus by Colorimetry
- 10200 H 2 ~ Chlorophyll a-b-c Determination by spectrophotometer
- 10200 H ~ Chlorophyll a-b-c Determination
- Color, APHA Platinum-Cobalt
- For determination of Copper by the Bicinchoninate method.
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
Impairment status from EPA ATTAINS 303(d) database
Lake size & watershed from HydroLAKES (HydroSHEDS)
Lake details from Minnesota DNR LakeFinder