Diamond Lake
Diamond Lake in Hennepin County, Minnesota has a water quality grade of D (Nutrient-rich). Phosphorus: 85.5 µg/L. Chlorophyll-a (algae): 12 µg/L. Maximum depth: 5.8 ft. Surface area: 51.71 acres.
- Typical in August
- 71°F
- Max depth
- 5.8 ft
- Area
- 52 acres
- Type
- Eutrophic
- Trend
- ↓ Declining
- Public access
- No
- Ice-out
- Mar 26
- Open water
- 261 days
Grade D 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 52-acre productive, nutrient-rich eutrophic lake in Hennepin County, Minnesota with a maximum depth of 6 feet (3-foot average). Water quality is graded D based on 2 sampling years through 2025. 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. Grade methodology: LakeGrade methodology.
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Swimming Safety
Grade onlyBacteria F
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.
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.
Water Quality Grade: D (Nutrient-rich)
No clarity data. Phosphorus level: 85.5 µg/L. Chlorophyll-a: 12 µg/L. Trophic State Index: 62.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | No recent samples | |
| Phosphorus | 85.5 µg/L | Poor |
| Chlorophyll-a (Algae) | 12 µg/L | Fair |
| Trophic State Index (TSI) | 62 | Eutrophic |
High nutrients, frequent algae, reduced 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
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Planning a whole trip? See where to stay at Minnesota’s top lakes →
Water Temperature
Diamond Lake typically sits around 71°F at the surface in August. 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.
Typical surface water temperature by month, from 138 field readings (2010–2025) via the EPA Water Quality Portal.
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | 5.8 ft |
| Average Depth | 3.2 ft |
| Surface Area | 52 acres |
| Shoreline Length | 1.2 mi |
| Littoral Zone | 100% |
| Public Access | No |
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS).
Fish Species
Click a species to see every graded lake where it is documented.
Fishing Diamond Lake
DNR Fisheries Survey Summary
1 survey on file from MN DNR Fisheries. Most recent: 1993-07-26 (Standard Survey).
Top Species by Catch Rate
| Species | Avg CPUE | Avg Weight |
|---|---|---|
| Black Bullhead | 6.78 | 0.11 lb |
| Bluegill | 5.22 | 0.11 lb |
| Common Carp | 4.11 | 2.44 lb |
| Green Sunfish | 3.00 | 0.09 lb |
| GOS | 1.33 | 0.06 lb |
| Hybrid Sunfish | 0.67 | 0.12 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
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
Water Quality Trend: ↓ Declining
Based on 6 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Phosphorus | → Stable | +0.2 µg/L/yr | 6 |
| Chlorophyll-a | ↓ Declining | +1.15 µg/L/yr | 6 |
Ice Season
Historical ice data from Minnesota DNR (14 observations).
Estimated open water season: 261 days
| Earliest | Latest | |
|---|---|---|
| Ice-Out | 2024-03-02 (2024) | 2023-04-12 (2023) |
| Ice-In | 2022-11-30 (2022) | 2015-12-19 (2015) |
Most recent ice-out: 2026-03-26
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 MN27-0022-00 · Official waterbody report
County Ranking
Ranked #35 of 81 lakes in Hennepin County
Nearby Lakes With Higher Grades
Diamond Lake holds Grade D. 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 D (Nutrient-rich). 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 works out to a bacteria swim-safety grade of F — a historical summary of past testing, not a current reading. Diamond Lake has a water quality grade of D (Nutrient-rich). Bacteria levels can spike quickly after heavy rain, so always check Minnesota's current beach and health-department advisories before you swim.
What is the water temperature of Diamond Lake?
- Diamond Lake typically sits around 71°F at the surface in August, 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.
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.
Explore Diamond Lake across LakeGrade
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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)
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
Ice data from Minnesota DNR Climate