Diamond Lake
Hennepin County, Minnesota405 acresView mapDirections
Minnesota PCA publishes the water-quality measurements for Diamond Lake. Here is what has been measured.
- Hypereutrophic
- Impaired · Nutrients (phosphorus, nitrogen)
- 8 ft max depth
- Public access
Diamond Lake in Hennepin County, Minnesota has water-quality measurements published by Minnesota PCA, shown here as reported. 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.
Minnesota DNR's Standard Survey on June 18, 1992 caught 106.00 black bullhead per gill net at Diamond Lake. DNR survey details →
Diamond Lake is a 405-acre highly nutrient-loaded hypereutrophic lake in Hennepin County, Minnesota with a maximum depth of 8 feet. 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. Methodology: how these readings are compared.
What Diamond Lake is good for
From access and monitoring records, not editorial picks.
- Boat launch1 documented ramp
Swimming conditions
Readings onlyRecreation use not supported
Based on clarity and algae readings from past sampling — there is no live water temperature and a current cyanobacteria reading for this lake. Check your state or county health department before you swim.
Nutrient and algae readings are not a swimming clearance. Diamond Lake is listed impaired under Clean Water Act §303(d) (IR 4A) for nutrients (phosphorus, nitrogen). Check local advisories before you swim.
Whether Diamond Lake is safe to swim in today is a call for the Minnesota Pollution Control Agency and the Minnesota DNR and the county health department, who post current advisories. LakeQuality does not issue swimming clearances.
Water quality measurements for Diamond Lake
These are the measurements Minnesota PCA publishes for Diamond Lake, shown as reported. The condition class beside each reading is the EPA National Lakes Assessment class for this lake’s ecoregion.
Very murky, less than 1.7 ft of visibility. Phosphorus 162.2 µg/L. Chlorophyll-a 66.5 µg/L. TSI 73.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | 1.7ft | Measured, not scored How deep a black-and-white disk stays visible from the surface. Higher is clearer. |
| Total phosphorus | 162µg/L | Poor GoodFairPoor |
| Chlorophyll-a (algae) | 66.5µg/L | Poor GoodFairPoor |
| Trophic state (TSI)Carlson's 0–100 index of how much algae a lake can support, from clarity, phosphorus and chlorophyll-a. | 73 | Hypereutrophic OligotrophicMesotrophicEutrophicHypereutrophic |
Very high nutrients, dense algae, poor clarity
Ask about Diamond Lake
Answers come straight from the public measurements and survey records on this page.
Water Temperature
Diamond Lake typically sits around 55°F at the surface in October. 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.
Column height runs from this lake’s coldest month (37°F) to its warmest (77°F).
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 →
Minnesota DNR's Standard Survey on June 18, 1992 caught 106.00 black bullhead per gill net at Diamond Lake.
A DNR fisheries survey reports fish abundance and catch rates, not water quality. LakeQuality shows Diamond Lake’s water-quality measurements separately, and the water-quality trend over 5 years of monitoring is improving. Catch rate is not a swim clearance and is not a weekly bite report.
DNR Fisheries Survey Summary
1 survey on file from MN DNR Fisheries. Most recent: 1992-06-18 (Standard Survey).
1 survey on file · most recent 1992-06-18 (Standard Survey)
34 years old| Species | Catch rate (CPUE) | Size | Avg weight |
|---|---|---|---|
| Black Bullhead | 421.75 | 0.15 lb |
CPUE = catch per unit effort, fish caught per net per set in a standardised survey. It measures abundance, not size, and is not a weekly bite report.
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
Lake Details
Max depth
8 ft
Surface area
405 acres
Shoreline
4.6 mi
Public access
Yes
Listed by Minnesota PCA
Lake Size & Watershed
Watershed (drainage) area
6 sq mi
HydroLAKES / HydroSHEDS
Elevation
886 ft
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS).
Recreation & Access
- Diamond LakePublic
Named access points in the USGS National Boat Ramps inventory, within about 3 miles. More lakes with boat ramps
Stays via Stay22
Stays 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 readings cover nutrients and algae, not lodging. Cabins and rentals around Diamond Lake are listed below.
Top-rated places to stay near Diamond Lake
Prices for Oct 9–11, 4 adults. Change dates on the map below.
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 →
Follow Diamond Lake’s readings
Email me when new measurements post for this lake. Updates stay free.
Or email
Fishing Diamond Lake
Water Quality Trend: Improving
Based on 5 years of monitoring (2020–2024).
Water clarity
Improving5 years
Phosphorus
Improving-27.79 µg/L/yr4 years
Chlorophyll-a
Improving-4.34 µg/L/yr4 years
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
Designated uses not supporting: Recreation.
A Total Maximum Daily Load (TMDL) plan has been approved.
Source: EPA ATTAINS assessment unit MN27-0125-00 · Official waterbody report
Nearby Lakes in Hennepin County
Frequently asked questions about Diamond Lake
Where is Diamond Lake?
- Diamond Lake is a lake in Hennepin County, Minnesota. Its water-quality measurements are published by Minnesota PCA and shown on this page as reported.
What is the water quality of Diamond Lake?
- Diamond Lake in Hennepin County, Minnesota has water-quality measurements published by Minnesota PCA, shown here as reported. 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?
- Nutrient and algae readings are not a swimming clearance. Diamond Lake is listed impaired under Clean Water Act §303(d) (IR 4A) for nutrients (phosphorus, nitrogen). Check local advisories before you swim.
What is the water temperature of Diamond Lake?
- Diamond Lake typically sits around 55°F at the surface in October, 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.
What did the DNR fisheries survey find at Diamond Lake?
- Minnesota DNR's Standard Survey on June 18, 1992 caught 106.00 black bullhead per gill net at Diamond Lake. A DNR fisheries survey reports fish abundance and catch rates, not water quality. LakeQuality shows Diamond Lake’s water-quality measurements separately, and the water-quality trend over 5 years of monitoring is improving. Catch rate is not a swim clearance and is not a weekly bite report.
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.
Can I fish at Diamond Lake?
- Diamond Lake has 1 documented boat landing in the USGS National Boat Ramps inventory. Seasons, size and bag limits, and whether you need a license are set by Minnesota's fish and wildlife agency, so check its current regulations before you go.
Explore Diamond Lake across LakeQuality
Fish species and the cleanest lakes across Minnesota
Fish species and best lakes in Hennepin County
Species activity outlook by water temperature and season
Where to stay at Minnesota's top lakes, each with its readings
Lakes in the Crow River Watershed, ranked by water quality
Minnesota's cleanest lakes, ranked on agency measurements
More lakes in Minnesota
State Parks Near Diamond Lake
Other Lakes in Minnesota
Hypereutrophic Lakes in Minnesota
Compare Diamond Lake With Nearby Lakes
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)
EPA condition classes from the National Lakes Assessment (EPA 841-R-24-006, Table 6-3), applied by ecoregion. See where the data comes from 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