Maple Lake
Maple Lake in Polk County, Minnesota has a water quality grade of C (Fair). Water clarity: 3.3 ft visibility. Phosphorus: 38.5 µg/L. Chlorophyll-a (algae): 17.8 µg/L. Maximum depth: 14 ft. Surface area: 1641.02 acres.
- Clarity
- 3.3 ft
- Typical in August
- 76°F
- Max depth
- 14 ft
- Area
- 1,641 acres
- Type
- Eutrophic
- Trend
- ↓ Declining
- Public access
- Yes
- Ice-out
- Apr 14
- Open water
- 227 days
Next lake in Polk County
Free interactive depth-contour map of Maple Lake, reaching a maximum surveyed depth of 10 ft. Toggle Depth contours to overlay the bathymetric survey lines. Contour data from Minnesota DNR.
Maple Lake is a 1,641-acre productive, nutrient-rich eutrophic lake in Polk County, Minnesota with a maximum depth of 14 feet. Water quality is graded C based on 2 sampling years through 2025. Overall water quality is declining over recent sampling years. The lake supports 12 documented fish species including black bullhead, black crappie, and bluegill. Public access is available with 1 public boat landing. Compared to the 18 other monitored lakes in Polk County, Maple Lake ranks #9 for water quality.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2025-09-04. 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.
Swim with caution, moderate algae may be present
Water Quality Grade: C (Fair)
Very murky, less than 3.3 ft of visibility. Phosphorus level: 38.5 µg/L. Chlorophyll-a: 17.8 µg/L. Trophic State Index: 59.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 3.3 ft | Not graded |
| Phosphorus | 38.5 µg/L | Fair |
| Chlorophyll-a (Algae) | 17.8 µg/L | Fair |
| Trophic State Index (TSI) | 59 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Where to stay near Maple Lake
Compare lakeside cabins, hotels, and vacation rentals near Maple Lake in Polk 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 Maple Lake
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Water Temperature
Maple Lake typically sits around 76°F at the surface in August. Summer average is about 74°F. Usually warmest in Jul (about 76°F) and coldest in May (about 54°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 17 field readings (2011–2021) via the EPA Water Quality Portal. See the full Maple Lake water temperature breakdown →
Blue-Green Algae (Cyanobacteria)
There’s no recent EPA CyAN cyanobacteria estimate for Maple Lake — clouds, ice, or an off-season gap in coverage. The most recent reading was high (570,164 cells/mL) on July 19, 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 |
|---|---|
| Maximum Depth | 14 ft |
| Surface Area | 1,641 acres |
| Shoreline Length | 19.8 mi |
| Littoral Zone | 96% |
| Public Access | Yes |
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS).
Recreation & Access
- Maple Lake WestPublic
Fish Species
Click a species to see every graded lake where it is documented.
Fishing Maple Lake
DNR Fisheries Survey Summary
12 surveys on file from MN DNR Fisheries. Most recent: 2024-06-24 (Targeted Survey).
Top Species by Catch Rate
| Species | Avg CPUE | Avg Weight |
|---|---|---|
| Black Bullhead | 50.77 | 0.42 lb |
| Spottail Shiner | 33.48 | — |
| Bluegill | 32.36 | 0.26 lb |
| Brown Bullhead | 26.41 | 0.64 lb |
| JND | 17.86 | — |
| Largemouth Bass | 15.92 | 0.85 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.
Black Bullhead
Bluegill
Brown Bullhead
Largemouth Bass
From the 2024-06-24 survey
Maple Lake is a 1,641-acre lake located in northern Polk County, two miles south of Mentor. The maximum depth is 15 feet and the shoreline is considered highly developed with homes and cabins. The lake receives heavy recreational use and angling pressure from the surrounding area. There are two public access points,…
DNR Reports & Resources
Minnesota DNR LakeFinder publishes lake survey, fish stocking, water access, and aquatic plant data for Maple Lake. 3 reports on file.
These links open on the official state DNR websites (Wisconsin DNR survey PDFs · Minnesota DNR LakeFinder).
- —Fisheries Lake Survey — MapleFisheries Lake Survey · MN DNR LakeFinder
- —Fish Stocking History — MapleFish Stocking History · MN DNR LakeFinder
- —Public Water Access Sites — MaplePublic Water Access Sites · MN DNR LakeFinder
Water Quality Trend: ↓ Declining
Based on 6 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | → Stable | 0 m/yr | 6 |
| Phosphorus | → Stable | +0.29 µg/L/yr | 6 |
| Chlorophyll-a | ↓ Declining | +1.19 µg/L/yr | 6 |
Ice Season
Historical ice data from Minnesota DNR (8 observations).
Estimated open water season: 227 days
| Earliest | Latest | |
|---|---|---|
| Ice-Out | 2017-04-06 (2017) | 2002-04-18 (2002) |
| Ice-In | 2003-11-16 (2003) | 2006-11-30 (2006) |
Most recent ice-out: 2017-04-06
Reservoir Info (USACE NID)
Maple Lake is a man-made reservoir impounded by the Maple Lake (completed 1942), built primarily for recreation on the Cyr Creek; gravity-type dam, 8 ft tall and 50 ft long.
- Surface area
- 1,477 ac
- Normal storage
- 11,872 ac-ft
- Max storage
- 20,352 ac-ft
- Drainage area
- 15.1 sq mi
- Hazard class
- Low
- Owner
- County of Polk
Source: USACE National Inventory of Dams, NID ID MN00222 · Operator website
EPA Impairment Status
Maple 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 MN60-0305-00 · Official waterbody report
County Ranking
Ranked #9 of 19 lakes in Polk County
Nearby Lakes With Higher Grades
Maple 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 Polk County
Frequently asked questions about Maple Lake
What is the water quality grade for Maple Lake?
- Maple Lake in Polk County, Minnesota has a water quality grade of C (Fair). Water clarity: 3.3 ft visibility. Phosphorus: 38.5 µg/L. Chlorophyll-a (algae): 17.8 µg/L. Maximum depth: 14 ft. Surface area: 1641.02 acres.
Is Maple Lake safe to swim in?
- Swim with caution, moderate algae may be present. Maple Lake has a water quality grade of C (Fair). Algae concentration (chlorophyll-a) is 17.8 µg/L. Always check local health department advisories before swimming.
What is the water temperature of Maple Lake?
- Maple Lake typically sits around 76°F at the surface in August, from 17 EPA Water Quality Portal field readings (2011–2021). That is a typical value for the month, not a live reading.
How deep is Maple Lake?
- Maple Lake has a maximum depth of 14 feet. The lake covers 1641.02 acres.
What fish are in Maple Lake?
- Fish species found in Maple Lake include black bullhead, black crappie, bluegill, brown bullhead, common carp, freshwater drum, largemouth bass, northern pike, pumpkinseed, walleye, white sucker, yellow perch. Maple Lake is located in Polk County, Minnesota.
When does Maple Lake thaw?
- Maple Lake typically has ice-out around Apr 14. Ice typically forms around Nov 27. The open water season is approximately 227 days.
Does Maple Lake have blue-green algae?
- There is no recent EPA CyAN cyanobacteria estimate for Maple Lake (clouds, ice, or an off-season gap). The most recent reading was high (570,164 cells/mL). Blue-green algae can appear and clear within days, so check Minnesota's current advisory before swimming.
Are there boat ramps on Maple Lake?
- Maple Lake has 1 documented boat landing in the USGS National Boat Ramps inventory. Named access points include Maple Lake West. Public access is listed as yes.
Explore Maple Lake across LakeGrade
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Where this data comes from
271 measurements from 4 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
MNPCA271 samples · 2020–2025
Analytical methods
- Field measurement/observation, generic method
- Phosphorus by Two Reagent Colorimetry
- 10200 H ~ Chlorophyll a-b-c Determination
Monitoring station identifiers (4)
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
Ice data from Minnesota DNR Climate