Square Lake
Square Lake in Washington County, Minnesota has a water quality grade of A (Excellent). Water clarity: 17 ft visibility. Phosphorus: 9 µg/L. Chlorophyll-a (algae): 2.9 µg/L. Maximum depth: 68 ft. Surface area: 203.05 acres.
- Clarity
- 17 ft
- Typical in August
- 60°F
- Max depth
- 68 ft
- Area
- 203 acres
- Type
- Oligotrophic
- Trend
- → Stable
- Public access
- Yes
Next lake in Washington County
Square Lake is a 203-acre cold, clear oligotrophic lake in Washington County, Minnesota with a maximum depth of 68 feet. Water quality is graded A based on 2 sampling years through 2025. Phosphorus level is declining over recent sampling years. The lake supports 9 documented fish species including bluegill, green sunfish, and hybrid sunfish. Public access is available with 1 public boat landing. Compared to the 74 other monitored lakes in Washington County, Square Lake ranks #3 for water quality.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2025-09-17. 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)
Crystal clear, you can see 17 ft down. Phosphorus level: 9 µg/L. Chlorophyll-a: 2.9 µg/L. Trophic State Index: 38.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 17 ft | Not graded |
| Phosphorus | 9 µg/L | Good |
| Chlorophyll-a (Algae) | 2.9 µg/L | Good |
| Trophic State Index (TSI) | 38 | Oligotrophic |
Low nutrients, clear water, excellent for swimming
Where to stay near Square Lake
Compare lakeside cabins, hotels, and vacation rentals near Square 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.
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Water Temperature
Square Lake typically sits around 60°F at the surface in August. Summer average is about 58°F. Usually warmest in Aug (about 60°F) and coldest in Apr (about 41°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 683 field readings (2010–2025) via the EPA Water Quality Portal. See the full Square Lake water temperature breakdown →
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | 68 ft |
| Surface Area | 203 acres |
| Shoreline Length | 2.4 mi |
| Littoral Zone | 32% |
| Public Access | Yes |
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS).
Recreation & Access
- Square Lake County ParkPublic
Fish Species
Click a species to see every graded lake where it is documented.
Fishing Square Lake
DNR Fisheries Survey Summary
16 surveys on file from MN DNR Fisheries. Most recent: 2016-08-10 (Targeted Survey).
Top Species by Catch Rate
| Species | Avg CPUE | Avg Weight |
|---|---|---|
| Bluntnose Minnow | 538.79 | — |
| SFS | 374.50 | — |
| IOD | 59.07 | — |
| BKF | 23.64 | — |
| BNS | 22.39 | — |
| Bluegill | 20.55 | 0.22 lb |
CPUE = catch per unit effort, averaged across surveys (excludes juvenile shoreline seining). Higher CPUE = more abundant in standardized sampling.
Length Distributions
Number of fish caught at each inch class in the most recent survey that recorded lengths. Red dashed line marks an approximate trophy threshold for that species.
Bluegill
From the 2016-08-10 survey
Square Lake is a 203 acre, class 23 lake located in northeastern Washington County. The water quality in Square Lake is among the best in the Twin Cities metro area, a secchi disk reading in 2014 was 18.0 feet, and the lake supports a diverse near shore fish community. A near shore Index of Biotic Integrity survey…
DNR Reports & Resources
Minnesota DNR LakeFinder publishes lake survey, fish stocking, water access, and aquatic plant data for Square Lake. 2 reports on file.
These links open on the official state DNR websites (Wisconsin DNR survey PDFs · Minnesota DNR LakeFinder).
- —Fisheries Lake Survey — SquareFisheries Lake Survey · MN DNR LakeFinder
- —Public Water Access Sites — SquarePublic Water Access Sites · MN DNR LakeFinder
Water Quality Trend: → Stable
Based on 6 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | → Stable | +0.075 m/yr | 6 |
| Phosphorus | ↓ Declining | +1.75 µg/L/yr | 2 |
| Chlorophyll-a | ↑ Improving | -0.25 µg/L/yr | 2 |
EPA Impairment Status
Square 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 MN82-0046-00 · Official waterbody report
County Ranking
Ranked #3 of 75 lakes in Washington County
Nearby Lakes in Washington County
Frequently asked questions about Square Lake
What is the water quality grade for Square Lake?
- Square Lake in Washington County, Minnesota has a water quality grade of A (Excellent). Water clarity: 17 ft visibility. Phosphorus: 9 µg/L. Chlorophyll-a (algae): 2.9 µg/L. Maximum depth: 68 ft. Surface area: 203.05 acres.
Is Square Lake safe to swim in?
- Excellent for swimming, crystal clear water with minimal algae. Square Lake has a water quality grade of A (Excellent). Algae concentration (chlorophyll-a) is 2.9 µg/L. Always check local health department advisories before swimming.
What is the water temperature of Square Lake?
- Square Lake typically sits around 60°F at the surface in August, from 683 EPA Water Quality Portal field readings (2010–2025). That is a typical value for the month, not a live reading.
How deep is Square Lake?
- Square Lake has a maximum depth of 68 feet. The lake covers 203.05 acres.
What fish are in Square Lake?
- Fish species found in Square Lake include bluegill, green sunfish, hybrid sunfish, largemouth bass, northern pike, pumpkinseed, white sucker, yellow bullhead, yellow perch. Square Lake is located in Washington County, Minnesota.
Are there boat ramps on Square Lake?
- Square Lake has 1 documented boat landing in the USGS National Boat Ramps inventory. Named access points include Square Lake County Park. Public access is listed as yes.
Explore Square Lake across LakeGrade
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Species activity outlook by water temperature and season
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Where this data comes from
174 measurements from 2 monitoring stations, 2020–2025. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Minnesota Pollution Control Agency - Ambient Surface Water
MNPCA174 samples · 2020–2025
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 (2)
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