Diamond Lake
Diamond Lake in Hennepin County, Minnesota has a water quality grade of F (Algae-prone). Water clarity: 1.7 ft visibility. Phosphorus: 162.2 µg/L. Chlorophyll-a (algae): 66.5 µg/L. Maximum depth: 8 ft. Surface area: 405.02 acres.
- Clarity
- 1.7 ft
- Typical in August
- 74°F
- Max depth
- 8 ft
- Area
- 405 acres
- Type
- Hypereutrophic
- Trend
- ↑ Improving
- Public access
- Yes
Grade F measures nutrients and algae, not whether this is a good place for a cabin trip. Cabins and rentals near Diamond Lake →
Next lake in Hennepin County
Diamond Lake is a 405-acre highly nutrient-loaded hypereutrophic lake in Hennepin County, Minnesota with a maximum depth of 8 feet. Water quality is graded F based on 3 sampling years through 2024. Overall water quality is improving over recent sampling years. Limited fish-species data available. Public access is available with 1 public boat landing. Compared to the 80 other monitored lakes in Hennepin County, Diamond Lake ranks #66 for water quality.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2024-10-07. 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.
Algae and nutrients are often high — check current advisories before swimming. Skip the water if you see scum or a paint-like bloom
Water Quality Grade: F (Algae-prone)
Very murky, less than 1.7 ft of visibility. Phosphorus level: 162.2 µg/L. Chlorophyll-a: 66.5 µg/L. Trophic State Index: 73.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 1.7 ft | Not graded |
| Phosphorus | 162.2 µg/L | Poor |
| Chlorophyll-a (Algae) | 66.5 µg/L | Poor |
| Trophic State Index (TSI) | 73 | Hypereutrophic |
Very high nutrients, dense algae, poor clarity
Where to stay near Diamond Lake
Compare lakeside cabins, hotels, and vacation rentals near Diamond Lake in Hennepin 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 Diamond Lake are listed below.
Top-rated places to stay near Diamond 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
Diamond Lake typically sits around 74°F at the surface in August. Summer average is about 74°F. Usually warmest in Jul (about 77°F) and coldest in Jan (about 37°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 395 field readings (2010–2024) via the EPA Water Quality Portal. See the full Diamond Lake water temperature breakdown →
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | 8 ft |
| Surface Area | 405 acres |
| Shoreline Length | 4.6 mi |
| Littoral Zone | 100% |
| Public Access | Yes |
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS).
Recreation & Access
- Diamond LakePublic
Fishing Diamond Lake
DNR Fisheries Survey Summary
1 survey on file from MN DNR Fisheries. Most recent: 1992-06-18 (Standard Survey).
Top Species by Catch Rate
| Species | Avg CPUE | Avg Weight |
|---|---|---|
| Black Bullhead | 421.75 | 0.15 lb |
CPUE = catch per unit effort, averaged across surveys (excludes juvenile shoreline seining). Higher CPUE = more abundant in standardized sampling.
From the 1992-06-18 survey
BLB AND FHM DOMINATE THE FISH POPULATION, WITH BLB CAPTURED IN NUMBERS AND POUNDS GREATLY EXCEEDING THE STATE AND LOCAL MEDIANS FOR TRAPNETS AND GILLNETS.
DNR Reports & Resources
Minnesota DNR LakeFinder publishes lake survey, fish stocking, water access, and aquatic plant data for Diamond Lake. 2 reports on file.
These links open on the official state DNR websites (Wisconsin DNR survey PDFs · Minnesota DNR LakeFinder).
- —Fisheries Lake Survey — DiamondFisheries Lake Survey · MN DNR LakeFinder
- —Public Water Access Sites — DiamondPublic Water Access Sites · MN DNR LakeFinder
Water Quality Trend: ↑ Improving
Based on 5 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↑ Improving | +0.082 m/yr | 5 |
| Phosphorus | ↑ Improving | -27.79 µg/L/yr | 4 |
| Chlorophyll-a | ↑ Improving | -4.34 µg/L/yr | 4 |
EPA Impairment Status
Diamond 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 MN27-0125-00 · Official waterbody report
County Ranking
Ranked #66 of 81 lakes in Hennepin County
Nearby Lakes With Higher Grades
Diamond Lake holds Grade F. 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 Hennepin County
Frequently asked questions about Diamond Lake
What is the water quality grade for Diamond Lake?
- Diamond Lake in Hennepin County, Minnesota has a water quality grade of F (Algae-prone). Water clarity: 1.7 ft visibility. Phosphorus: 162.2 µg/L. Chlorophyll-a (algae): 66.5 µg/L. Maximum depth: 8 ft. Surface area: 405.02 acres.
Is Diamond Lake safe to swim in?
- Algae and nutrients are often high — check current advisories before swimming. Skip the water if you see scum or a paint-like bloom. Diamond Lake has a water quality grade of F (Algae-prone). Algae concentration (chlorophyll-a) is 66.5 µg/L. Always check local health department advisories before swimming.
What is the water temperature of Diamond Lake?
- Diamond Lake typically sits around 74°F at the surface in August, from 395 EPA Water Quality Portal field readings (2010–2024). That is a typical value for the month, not a live reading.
How deep is Diamond Lake?
- Diamond Lake has a maximum depth of 8 feet. The lake covers 405.02 acres.
Are there boat ramps on Diamond Lake?
- Diamond Lake has 1 documented boat landing in the USGS National Boat Ramps inventory. Named access points include Diamond Lake. Public access is listed as yes.
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Where this data comes from
204 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
MNPCA204 samples · 2020–2024
Analytical methods
- Field measurement/observation, generic method
- Phosphorus by Two Reagent Colorimetry
- 10200 H ~ Chlorophyll a-b-c Determination
- 4500 N C ~ Persufate Method for Total Nitrogen
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