Blue Lake
Blue Lake in Isanti County, Minnesota has a water quality grade of D (Nutrient-rich). Water clarity: 8.9 ft visibility. Phosphorus: 44 µg/L. Chlorophyll-a (algae): 21.4 µg/L. Maximum depth: 31 ft. Surface area: 295.99 acres.
- Clarity
- 8.9 ft
- Typical in August
- 76°F
- Max depth
- 31 ft
- Area
- 296 acres
- Type
- Eutrophic
- Trend
- ↑ Improving
- Public access
- Yes
Grade D measures nutrients and algae, not whether this is a good place for a cabin trip. Cabins and rentals near Blue Lake →
Next lake in Isanti County
Blue Lake is a 296-acre productive, nutrient-rich eutrophic lake in Isanti County, Minnesota with a maximum depth of 31 feet. Water quality is graded D based on 2 sampling years through 2025. Overall water quality is improving over recent sampling years. The lake supports 13 documented fish species including black bullhead, black crappie, and bluegill. Public access is available with 2 public boat landings. Compared to the 16 other monitored lakes in Isanti County, Blue Lake ranks #11 for water quality.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2025-10-08. Grade methodology: LakeGrade methodology.
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Swimming Safety
Grade onlyAlgae risk
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.
Nutrients and algae run higher than average — check local advisories before swimming, and skip the water if you see scum
Water Quality Grade: D (Nutrient-rich)
Moderate clarity, visible to about 8.9 ft. Phosphorus level: 44 µg/L. Chlorophyll-a: 21.4 µg/L. Trophic State Index: 55.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 8.9 ft | Not graded |
| Phosphorus | 44 µg/L | Poor |
| Chlorophyll-a (Algae) | 21.4 µg/L | Poor |
| Trophic State Index (TSI) | 55 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Where to stay near Blue Lake
Compare lakeside cabins, hotels, and vacation rentals near Blue Lake in Isanti 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. The water-quality grade measures nutrients and algae, not lodging — cabins and rentals around Blue Lake are listed below.
Top-rated places to stay near Blue Lake
Availability and prices from Stay22 partners (Booking.com, Vrbo, Expedia). We may earn a commission from bookings, at no extra cost to you.
Planning a whole trip? See where to stay at Minnesota’s top lakes →
Water Temperature
Blue Lake typically sits around 76°F at the surface in August. Summer average is about 76°F. Usually warmest in Jul (about 79°F) and coldest in Oct (about 57°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 154 field readings (2016–2025) via the EPA Water Quality Portal. See the full Blue Lake water temperature breakdown →
Blue-Green Algae (Cyanobacteria)
There’s no recent EPA CyAN cyanobacteria estimate for Blue Lake — clouds, ice, or an off-season gap in coverage. The most recent reading was very high (1,047,129 cells/mL) on September 28, 2024.
Blue-green algae can appear and clear within days, so check your state’s current advisory before swimming. EPA CyAN ↗
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | 31 ft |
| Surface Area | 296 acres |
| Shoreline Length | 6.4 mi |
| Littoral Zone | 45% |
| Public Access | Yes |
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS).
Recreation & Access
- Blue Lake (North)Public
- Blue Lake (East)Public
Fish Species
Click a species to see every graded lake where it is documented.
Fishing Blue Lake
DNR Fisheries Survey Summary
11 surveys on file from MN DNR Fisheries. Most recent: 2025-05-12 (Targeted Survey).
Top Species by Catch Rate
| Species | Avg CPUE | Avg Weight |
|---|---|---|
| Black Crappie | 85.95 | 0.19 lb |
| Largemouth Bass | 22.58 | 0.84 lb |
| Bluegill | 20.44 | 0.14 lb |
| Bluntnose Minnow | 19.27 | — |
| Yellow Perch | 10.59 | 0.11 lb |
| JND | 10.58 | — |
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.
Black Crappie
Largemouth Bass
Bluegill
Yellow Perch
From the 2025-05-12 survey
Blue Lake is a 263-acre lake in southwest Isanti County located five miles northeast of Zimmerman and is within the Rum River watershed. It has a maximum depth of 31 feet and 51 percent of the lake is less than 15 feet deep (134 acres). Water clarity in May and June can be 6 to 9 feet; however, it becomes low in…
DNR Reports & Resources
Minnesota DNR LakeFinder publishes lake survey, fish stocking, water access, and aquatic plant data for Blue Lake. 4 reports on file.
These links open on the official state DNR websites (Wisconsin DNR survey PDFs · Minnesota DNR LakeFinder).
- —Fisheries Lake Survey — BlueFisheries Lake Survey · MN DNR LakeFinder
- —Aquatic Plant Report — Blue (1850)Aquatic Plant Report · MN DNR LakeFinder
- —Fish Stocking History — BlueFish Stocking History · MN DNR LakeFinder
- —Public Water Access Sites — BluePublic Water Access Sites · MN DNR LakeFinder
Water Quality Trend: ↑ Improving
Based on 6 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↓ Declining | -0.375 m/yr | 6 |
| Phosphorus | ↑ Improving | -12.75 µg/L/yr | 4 |
| Chlorophyll-a | ↑ Improving | -6.87 µg/L/yr | 4 |
EPA Impairment Status
Blue 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 MN30-0114-00 · Official waterbody report · Matched by proximity (2.3 km)
County Ranking
Ranked #11 of 17 lakes in Isanti County
Nearby Lakes With Higher Grades
Blue Lake holds Grade D. 2 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 Isanti County
Frequently asked questions about Blue Lake
What is the water quality grade for Blue Lake?
- Blue Lake in Isanti County, Minnesota has a water quality grade of D (Nutrient-rich). Water clarity: 8.9 ft visibility. Phosphorus: 44 µg/L. Chlorophyll-a (algae): 21.4 µg/L. Maximum depth: 31 ft. Surface area: 295.99 acres.
Is Blue Lake safe to swim in?
- Nutrients and algae run higher than average — check local advisories before swimming, and skip the water if you see scum. Blue Lake has a water quality grade of D (Nutrient-rich). Algae concentration (chlorophyll-a) is 21.4 µg/L. Always check local health department advisories before swimming.
What is the water temperature of Blue Lake?
- Blue Lake typically sits around 76°F at the surface in August, from 154 EPA Water Quality Portal field readings (2016–2025). That is a typical value for the month, not a live reading.
How deep is Blue Lake?
- Blue Lake has a maximum depth of 31 feet. The lake covers 295.99 acres.
What fish are in Blue Lake?
- Fish species found in Blue Lake include black bullhead, black crappie, bluegill, bowfin (dogfish), green sunfish, hybrid sunfish, largemouth bass, northern pike, pumpkinseed, walleye, white sucker, yellow bullhead, yellow perch. Blue Lake is located in Isanti County, Minnesota.
Does Blue Lake have blue-green algae?
- There is no recent EPA CyAN cyanobacteria estimate for Blue Lake (clouds, ice, or an off-season gap). The most recent reading was very high (1,047,129 cells/mL). Blue-green algae can appear and clear within days, so check Minnesota's current advisory before swimming.
Are there boat ramps on Blue Lake?
- Blue Lake has 2 documented boat landings in the USGS National Boat Ramps inventory. Named access points include Blue Lake (North), Blue Lake (East). Public access is listed as yes.
Explore Blue Lake across LakeGrade
Fish species and top-graded lakes across Minnesota
Fish species and best lakes in Isanti County
Species activity outlook by water temperature and season
Where to stay at Minnesota's top lakes, each with its grade
Lakes in the Rum River Watershed, ranked by water quality
High nutrients, frequent algae, reduced clarity
Minnesota's cleanest and most-polluted lakes, ranked
More Minnesota Lake Rankings
Other Grade D Lakes in Minnesota
Eutrophic Lakes in Minnesota
Where this data comes from
276 measurements from 2 monitoring stations, 2022–2025. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Minnesota Pollution Control Agency - Ambient Surface Water
MNPCA276 samples · 2022–2025
Analytical methods
- Field measurement/observation, generic method
- Phosphorus by Colorimetry
- 10200 H ~ Chlorophyll a-b-c Determination
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