Diamond Lake
Hennepin County, Minnesota52 acresView mapDirections
Minnesota PCA publishes the water-quality measurements for Diamond Lake. Here is what has been measured.
- Eutrophic
- 6 ft max depth
Diamond Lake in Hennepin County, Minnesota has water-quality measurements published by Minnesota PCA, shown here as reported. Phosphorus: 85.5 µg/L. Chlorophyll-a (algae): 12 µg/L. Maximum depth: 5.8 ft. Surface area: 51.71 acres.
Minnesota DNR's Standard Survey on July 26, 1993 caught 0.11 black crappie per trap net at Diamond Lake. DNR survey details →
Diamond Lake is a 52-acre productive, nutrient-rich eutrophic lake in Hennepin County, Minnesota with a maximum depth of 6 feet (3-foot average). Overall water quality is declining over recent sampling years. The lake supports 7 documented fish species including black bullhead, black crappie, and bluegill. No public access — the lake is private or restricted. Compared to the 80 other monitored lakes in Hennepin County, Diamond Lake ranks #35 for water quality.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2025-10-23. Methodology: how these readings are compared.
Diamond Lake covers about 52 acres in Hennepin County. The median ice-out date is March 26, which is when the open-water season begins. Vrbo is where to look for cabins and lake homes around Diamond Lake, and Booking.com and Expedia search hotels near the lake for your dates.
What Diamond Lake is good for
From access and monitoring records, not editorial picks.
- Fishing7 species recorded
- Ice seasonIce-out around Mar 26
Swimming conditions
Readings onlyBacteria tested: exceedances
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.
Based on E. coli testing, Diamond Lake routinely exceeded the EPA safe-swimming threshold (235 MPN/100mL) — on 33.3% of 6 samples across 6 seasons.
This is a historical summary of past testing, not a current condition — bacteria levels change quickly, especially after rain. Always check Minnesota’s current beach and health-department advisories before swimming.
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.
No clarity data. Phosphorus 85.5 µg/L. Chlorophyll-a 12 µg/L. TSI 62.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | No reading How deep a black-and-white disk stays visible from the surface. Higher is clearer. | |
| Total phosphorus | 85.5µg/L | Poor GoodFairPoor |
| Chlorophyll-a (algae) | 12µg/L | Fair GoodFairPoor |
| Trophic state (TSI)Carlson's 0–100 index of how much algae a lake can support, from clarity, phosphorus and chlorophyll-a. | 62 | Eutrophic OligotrophicMesotrophicEutrophicHypereutrophic |
High nutrients, frequent algae, reduced 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 51°F at the surface in October. Summer average is about 73°F. Usually warmest in Jul (about 74°F) and coldest in Jan (about 33°F). These are typical values by month — not a live reading.
Column height runs from this lake’s coldest month (33°F) to its warmest (74°F).
Typical surface water temperature by month, from 138 field readings (2010–2025) via the EPA Water Quality Portal.
Minnesota DNR's Standard Survey on July 26, 1993 caught 0.11 black crappie per trap 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 6 years of monitoring is declining. 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: 1993-07-26 (Standard Survey).
1 survey on file · most recent 1993-07-26 (Standard Survey)
33 years old| Species | Catch rate (CPUE) | Size | Avg weight |
|---|---|---|---|
| Black Bullhead | 6.78 | 3–10 in 1993-07-26 | 0.11 lb |
| Bluegill | 5.22 | 3–7 in 1993-07-26 | 0.11 lb |
| Common Carp | 4.11 | 4–24 in 1993-07-26 | 2.44 lb |
| Green Sunfish | 3.00 | 3–6 in 1993-07-26 | 0.09 lb |
| Golden Shiner | 1.33 | 4–5 in 1993-07-26 | 0.06 lb |
| Hybrid Sunfish | 0.67 | 3–6 in 1993-07-26 | 0.12 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.
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
Common Carp
Green Sunfish
From the 1993-07-26 survey
The current fish population is dominated by black bullhead, carp, bluegill, and green sunfish. The bluegill population in Diamond lake is average compared to other lakes of the same classification. Their weight is considered slightly less than average. Over half of the bluegills measured were between 4 and 5.5 inches…
DNR Reports & Resources
Minnesota DNR LakeFinder publishes lake survey, fish stocking, water access, and aquatic plant data for Diamond Lake. 1 report 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
Lake Details
Max depth
5.8 ft
Average depth
3.2 ft
Surface area
52 acres
Shoreline
1.2 mi
Littoral zone
100%
Share shallower than 15 ft
Public access
No
Listed by Minnesota PCA
Lake Size & Watershed
Watershed (drainage) area
1 sq mi
HydroLAKES / HydroSHEDS
Elevation
810 ft
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS).
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 →
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Fish Species
Click a species to see every lake where it is documented.
Fishing Diamond Lake
Water Quality Trend: Worsening
Based on 6 years of monitoring (2020–2025).
Phosphorus
Stable+0.2 µg/L/yr6 years
Chlorophyll-a
Worsening+1.15 µg/L/yr6 years
Ice season
Typical ice-out
Mar 26
Earliest Mar 2, 2024 · Latest Apr 12, 2023
Typical ice-in
Dec 12
Earliest Nov 30, 2022 · Latest Dec 19, 2015
Most recent ice-out
Mar 26
2026
14 observations · Minnesota PCA ice records
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. Phosphorus: 85.5 µg/L. Chlorophyll-a (algae): 12 µg/L. Maximum depth: 5.8 ft. Surface area: 51.71 acres.
Is Diamond Lake safe to swim in?
- Based on E. coli testing, Diamond Lake routinely exceeded the EPA safe-swimming threshold (235 MPN/100mL) — on 33.3% of 6 samples across 6 seasons. That is a historical summary of past bacteria testing, not a current reading and not a swimming clearance. Bacteria levels can spike quickly after heavy rain, so whether Diamond Lake is safe to swim in today is a call for Minnesota's water agency and the county health department; check their current beach advisories before you swim.
What is the water temperature of Diamond Lake?
- Diamond Lake typically sits around 51°F at the surface in October, from 138 EPA Water Quality Portal field readings (2010–2025). That is a typical value for the month, not a live reading.
How deep is Diamond Lake?
- Diamond Lake has a maximum depth of 5.8 feet and an average depth of 3.2 feet. The lake covers 51.71 acres.
What fish are in Diamond Lake?
- Fish species found in Diamond Lake include black bullhead, black crappie, bluegill, common carp, green sunfish, hybrid sunfish, pumpkinseed. Diamond Lake is located in Hennepin County, Minnesota.
What did the DNR fisheries survey find at Diamond Lake?
- Minnesota DNR's Standard Survey on July 26, 1993 caught 0.11 black crappie per trap 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 6 years of monitoring is declining. Catch rate is not a swim clearance and is not a weekly bite report.
When does Diamond Lake thaw?
- Diamond Lake typically has ice-out around Mar 26. Ice typically forms around Dec 12. The open water season is approximately 261 days.
Can I fish at Diamond Lake?
- Public access to Diamond Lake is listed as no on the lake record, so confirm before you make the trip. 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
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Where this data comes from
191 measurements from 1 monitoring station, 2020–2025. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Minnesota Pollution Control Agency - Ambient Surface Water
MNPCA191 samples · 2020–2025
Analytical methods
- 4500 P E ~ Phosphorus in Water by Colorimetry- Ascorbic Acid Method
- 10200 H ~ Chlorophyll a-b-c Determination
- Turbidity, Nephelometric Method
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
Lake size & watershed from HydroLAKES (HydroSHEDS)
Lake details from Minnesota DNR LakeFinder
Ice data from Minnesota DNR Climate