Big Marine Lake
Big Marine Lake in Washington County, Minnesota has a water quality grade of A (Excellent). Water clarity: 12 ft visibility. Phosphorus: 13 µg/L. Chlorophyll-a (algae): 4.6 µg/L.
- Clarity
- 12 ft
- Typical in August
- 70°F
- Mean depth
- ~22 ft est.
- Type
- Mesotrophic
- Trend
- → Stable
- Public access
- Yes
Next lake in Washington County
Big Marine Lake is a mesotrophic lake in Washington County, Minnesota with an estimated average depth of about 22 feet. Water quality is graded A based on 2 sampling years through 2024. Water clarity is improving over recent sampling years. Limited fish-species data available. Public access is available with 3 public boat landings. Compared to the 74 other monitored lakes in Washington County, Big Marine Lake ranks #4 for water quality.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2024-10-25. Grade methodology: LakeGrade methodology.
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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.
Excellent for swimming, crystal clear water with minimal algae
Water Quality Grade: A (Excellent)
Good clarity, visible to about 12 ft. Phosphorus level: 13 µg/L. Chlorophyll-a: 4.6 µg/L. Trophic State Index: 43.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 12 ft | Not graded |
| Phosphorus | 13 µg/L | Good |
| Chlorophyll-a (Algae) | 4.6 µg/L | Good |
| Trophic State Index (TSI) | 43 | Mesotrophic |
Moderate nutrients, good water quality
Where to stay near Big Marine Lake
Compare lakeside cabins, hotels, and vacation rentals near Big Marine Lake in Washington 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 Big Marine Lake
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Water Temperature
Big Marine Lake typically sits around 70°F at the surface in August. Summer average is about 67°F. Usually warmest in Aug (about 70°F) and coldest in Apr (about 45°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 313 field readings (2010–2024) via the EPA Water Quality Portal. See the full Big Marine Lake water temperature breakdown →
Blue-Green Algae (Cyanobacteria)
There’s no recent EPA CyAN cyanobacteria estimate for Big Marine Lake — clouds, ice, or an off-season gap in coverage. The most recent reading was moderate (26,546 cells/mL) on April 11, 2026.
Blue-green algae can appear and clear within days, so check your state’s current advisory before swimming. EPA CyAN ↗
Lake Details
| Characteristic | Value |
|---|---|
| Average Depth | ~22 ft est. |
| Public Access | Yes |
Depth marked “est.” is a modeled estimate from HydroLAKES, not a measured survey. Minnesota has not published bathymetry for Big Marine 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.
Recreation & Access
- Big Marine Lake (South)Public
- Big Marine Park ReservePublic
- Veterans CampgroundPublic
Fishing Big Marine Lake
Invasive & Introduced Species
Red chips are ecologically harmful invasive species. Gray chips are stocked or introduced fish that aren't a current ecological concern.
DNR Reports & Resources
Minnesota DNR LakeFinder publishes lake survey, fish stocking, water access, and aquatic plant data for Big Marine Lake. 1 report on file.
These links open on the official state DNR websites (Wisconsin DNR survey PDFs · Minnesota DNR LakeFinder).
- —Public Water Access Sites — Big Marine (Main Lake)Public Water Access Sites · MN DNR LakeFinder
Water Quality Trend: → Stable
Based on 3 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↑ Improving | +0.077 m/yr | 3 |
| Phosphorus | → Stable | -0.37 µg/L/yr | 3 |
| Chlorophyll-a | ↓ Declining | +0.15 µg/L/yr | 3 |
EPA Impairment Status
Big Marine Lake is officially listed as impaired under Clean Water Act §303(d) in the 2024 EPA reporting cycle (IR category 4A).
Causes of impairment
A Total Maximum Daily Load (TMDL) plan has been approved.
Source: EPA ATTAINS assessment unit MN82-0052-04 · Official waterbody report · Matched by proximity (1.88 km)
County Ranking
Ranked #4 of 75 lakes in Washington County
Nearby Lakes in Washington County
Frequently asked questions about Big Marine Lake
What is the water quality grade for Big Marine Lake?
- Big Marine Lake in Washington County, Minnesota has a water quality grade of A (Excellent). Water clarity: 12 ft visibility. Phosphorus: 13 µg/L. Chlorophyll-a (algae): 4.6 µg/L.
Is Big Marine Lake safe to swim in?
- Excellent for swimming, crystal clear water with minimal algae. Big Marine Lake has a water quality grade of A (Excellent). Algae concentration (chlorophyll-a) is 4.6 µg/L. Always check local health department advisories before swimming.
What is the water temperature of Big Marine Lake?
- Big Marine Lake typically sits around 70°F at the surface in August, from 313 EPA Water Quality Portal field readings (2010–2024). That is a typical value for the month, not a live reading.
How deep is Big Marine Lake?
- No published bathymetric survey covers Big Marine Lake, so its depth has not been measured. The HydroLAKES global model estimates an average depth of about 22 feet, but that is a modelled estimate derived from surrounding terrain rather than a measurement on the water, so treat it as approximate.
Does Big Marine Lake have blue-green algae?
- There is no recent EPA CyAN cyanobacteria estimate for Big Marine Lake (clouds, ice, or an off-season gap). The most recent reading was moderate (26,546 cells/mL). Blue-green algae can appear and clear within days, so check Minnesota's current advisory before swimming.
Are there boat ramps on Big Marine Lake?
- Big Marine Lake has 3 documented boat landings in the USGS National Boat Ramps inventory. Named access points include Big Marine Lake (South), Big Marine Park Reserve, Veterans Campground. Public access is listed as yes.
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Where this data comes from
102 measurements from 1 monitoring station, 2020–2024. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Minnesota Pollution Control Agency - Ambient Surface Water
MNPCA102 samples · 2020–2024
Analytical methods
- Field measurement/observation, generic method
- Total Phosphorus After Block Digestion
- Phosphorus by Colorimetry
- Analysis of Chlorophyll in Periphyton and Plankton
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
Named boat-access points from the USGS National Boat Ramps inventory