Fannie Lake
Fannie Lake in Isanti County, Minnesota has a water quality grade of C (Fair). Water clarity: 6.9 ft visibility. Phosphorus: 35 µg/L. Chlorophyll-a (algae): 9.3 µg/L. Maximum depth: 33 ft. Surface area: 360.01 acres.
- Clarity
- 6.9 ft
- Typical in August
- 77°F
- Max depth
- 33 ft
- Area
- 360 acres
- Type
- Eutrophic
- Trend
- ↑ Improving
- Public access
- Yes
Next lake in Isanti County
Fannie Lake is a 360-acre productive, nutrient-rich eutrophic lake in Isanti County, Minnesota with a maximum depth of 33 feet. Water quality is graded C 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, Fannie Lake ranks #8 for water quality.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2025-09-17. Grade methodology: LakeGrade methodology.
Watch Fannie 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)
Moderate clarity, visible to about 6.9 ft. Phosphorus level: 35 µg/L. Chlorophyll-a: 9.3 µg/L. Trophic State Index: 52.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 6.9 ft | Not graded |
| Phosphorus | 35 µg/L | Fair |
| Chlorophyll-a (Algae) | 9.3 µg/L | Fair |
| Trophic State Index (TSI) | 52 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Where to stay near Fannie Lake
Compare lakeside cabins, hotels, and vacation rentals near Fannie 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.
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Water Temperature
Fannie Lake typically sits around 77°F at the surface in August. Summer average is about 76°F. Usually warmest in Jul (about 79°F) and coldest in May (about 61°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 18 field readings (2016–2025) via the EPA Water Quality Portal. See the full Fannie Lake water temperature breakdown →
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | 33 ft |
| Surface Area | 360 acres |
| Shoreline Length | 6 mi |
| Littoral Zone | 85% |
| Public Access | Yes |
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS).
Recreation & Access
- Lake Fannie (Northeast)Public
- Fannie Lake (East)Public
Fish Species
Click a species to see every graded lake where it is documented.
Fishing Fannie 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 Fisheries Survey Summary
10 surveys on file from MN DNR Fisheries. Most recent: 2022-06-27 (Targeted Survey).
Top Species by Catch Rate
| Species | Avg CPUE | Avg Weight |
|---|---|---|
| Bluegill | 39.64 | 0.14 lb |
| Black Bullhead | 15.66 | 0.6 lb |
| Largemouth Bass | 14.98 | 1.03 lb |
| Black Crappie | 6.99 | 0.18 lb |
| Yellow Perch | 5.06 | 0.09 lb |
| GOS | 4.26 | 0.04 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
Black Bullhead
Largemouth Bass
Black Crappie
From the 2022-06-27 survey
Fannie Lake is a 366-acre lake located in Isanti County that has been assigned to lake class 34. The lake is managed primarily for Northern Pike, Largemouth Bass, Black Crappie, and Bluegill. To assess the current population, a population assessment was conducted from June 27 to 30, 2022 with standard lake survey…
DNR Reports & Resources
Minnesota DNR LakeFinder publishes lake survey, fish stocking, water access, and aquatic plant data for Fannie Lake. 4 reports on file.
These links open on the official state DNR websites (Wisconsin DNR survey PDFs · Minnesota DNR LakeFinder).
- —Fisheries Lake Survey — FannieFisheries Lake Survey · MN DNR LakeFinder
- —Aquatic Plant Report — Fannie (1854)Aquatic Plant Report · MN DNR LakeFinder
- —Fish Stocking History — FannieFish Stocking History · MN DNR LakeFinder
- —Public Water Access Sites — FanniePublic 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 | → Stable | +0.026 m/yr | 6 |
| Phosphorus | → Stable | +0.25 µg/L/yr | 4 |
| Chlorophyll-a | ↑ Improving | -1.34 µg/L/yr | 4 |
EPA Impairment Status
Fannie 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 MN30-0043-00 · Official waterbody report
County Ranking
Ranked #8 of 17 lakes in Isanti County
Nearby Lakes With Higher Grades
Fannie Lake holds Grade C. One nearby lake has a higher nutrient-and-algae grade — useful for a swim day, not a reason to skip lodging here.
See full comparison →Nearby Lakes in Isanti County
Frequently asked questions about Fannie Lake
What is the water quality grade for Fannie Lake?
- Fannie Lake in Isanti County, Minnesota has a water quality grade of C (Fair). Water clarity: 6.9 ft visibility. Phosphorus: 35 µg/L. Chlorophyll-a (algae): 9.3 µg/L. Maximum depth: 33 ft. Surface area: 360.01 acres.
Is Fannie Lake safe to swim in?
- Generally safe for swimming, moderate water quality. Fannie Lake has a water quality grade of C (Fair). Algae concentration (chlorophyll-a) is 9.3 µg/L. Always check local health department advisories before swimming.
What is the water temperature of Fannie Lake?
- Fannie Lake typically sits around 77°F at the surface in August, from 18 EPA Water Quality Portal field readings (2016–2025). That is a typical value for the month, not a live reading.
How deep is Fannie Lake?
- Fannie Lake has a maximum depth of 33 feet. The lake covers 360.01 acres.
What fish are in Fannie Lake?
- Fish species found in Fannie 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. Fannie Lake is located in Isanti County, Minnesota.
Are there boat ramps on Fannie Lake?
- Fannie Lake has 2 documented boat landings in the USGS National Boat Ramps inventory. Named access points include Lake Fannie (Northeast), Fannie Lake (East). Public access is listed as yes.
Explore Fannie Lake across LakeGrade
Depth, room, public access, and the state wake-sport rules
Fish species and top-graded lakes across Minnesota
Fish species and best lakes in Isanti County
Species activity outlook by water temperature and season
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Lakes in the Rum River Watershed, ranked by water quality
High nutrients, frequent algae, reduced clarity
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State Parks Near Fannie Lake
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Where this data comes from
38 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
MNPCA38 samples · 2022–2025
Analytical methods
- Field measurement/observation, generic method
- Phosphorus by Two Reagent Colorimetry
- 10200 H ~ Chlorophyll a-b-c Determination
- Phosphorus by Colorimetry
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