Riley Lake
Riley Lake in Hennepin County, Minnesota has a water quality grade of A (Excellent). Water clarity: 11.5 ft visibility. Phosphorus: 24 µg/L. Chlorophyll-a (algae): 6.5 µg/L. Maximum depth: 49 ft. Surface area: 296.21 acres.
- Clarity
- 11.5 ft
- Typical in August
- 63°F
- Max depth
- 49 ft
- Area
- 296 acres
- Type
- Mesotrophic
- Trend
- ↓ Declining
- Public access
- Yes
- Ice-out
- Apr 5
Next lake in Hennepin County
Riley Lake is a 296-acre mesotrophic lake in Hennepin County, Minnesota with a maximum depth of 49 feet (21-foot average). Water quality is graded A based on 2 sampling years through 2025. Overall water quality is declining over recent sampling years. The lake supports 11 documented fish species including black bullhead, black crappie, and bluegill. Public access is available with 1 public boat landing. Compared to the 80 other monitored lakes in Hennepin County, Riley Lake ranks #4 for water quality.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2025-10-13. Grade methodology: LakeGrade methodology.
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Swimming Safety
Grade onlyLow algae
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.
Excellent for swimming, crystal clear water with minimal algae
Water Quality Grade: A (Excellent)
Good clarity, visible to about 11.5 ft. Phosphorus level: 24 µg/L. Chlorophyll-a: 6.5 µg/L. Trophic State Index: 47.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 11.5 ft | Not graded |
| Phosphorus | 24 µg/L | Good |
| Chlorophyll-a (Algae) | 6.5 µg/L | Good |
| Trophic State Index (TSI) | 47 | Mesotrophic |
Moderate nutrients, good water quality
Where to stay near Riley Lake
Compare lakeside cabins, hotels, and vacation rentals near Riley 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.
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Water Temperature
Riley Lake typically sits around 63°F at the surface in August. Summer average is about 62°F. Usually warmest in Jul (about 63°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 1,474 field readings (2010–2025) via the EPA Water Quality Portal. See the full Riley Lake water temperature breakdown →
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | 49 ft |
| Average Depth | 21 ft |
| Surface Area | 296 acres |
| Shoreline Length | 3.3 mi |
| Littoral Zone | 37% |
| Public Access | Yes |
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS).
Recreation & Access
- Riley LakePublic
Fish Species
Click a species to see every graded lake where it is documented.
Fishing Riley Lake
Invasive & Introduced Species
Red chips are ecologically harmful invasive species. Gray chips are stocked or introduced fish that aren't a current ecological concern.
DNR Fisheries Survey Summary
10 surveys on file from MN DNR Fisheries. Most recent: 2021-06-22 (Standard Survey).
Top Species by Catch Rate
| Species | Avg CPUE | Avg Weight |
|---|---|---|
| Black Bullhead | 48.32 | 0.54 lb |
| Bluegill | 34.44 | 0.21 lb |
| Black Crappie | 15.82 | 0.24 lb |
| Yellow Perch | 13.72 | 0.13 lb |
| Brown Bullhead | 7.89 | 0.71 lb |
| Northern Pike | 6.92 | 3.95 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
Black Crappie
Yellow Perch
From the 2021-06-22 survey
Lake Riley is a 296-acre lake with a maximum depth of 49 feet. The lake is located west of Eden Prairie, and Walleye are stocked each year by the lake association. During the summer of 2021, water clarity was neither extremely high nor extremely low, and the lake held good levels of dissolved oxygen to a depth of 32…
DNR Reports & Resources
Minnesota DNR LakeFinder publishes lake survey, fish stocking, water access, and aquatic plant data for Riley Lake. 3 reports on file.
These links open on the official state DNR websites (Wisconsin DNR survey PDFs · Minnesota DNR LakeFinder).
- —Fisheries Lake Survey — RileyFisheries Lake Survey · MN DNR LakeFinder
- —Fish Stocking History — RileyFish Stocking History · MN DNR LakeFinder
- —Public Water Access Sites — RileyPublic 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 | ↓ Declining | -0.552 m/yr | 6 |
| Phosphorus | ↓ Declining | +3.89 µg/L/yr | 5 |
| Chlorophyll-a | ↓ Declining | +3.54 µg/L/yr | 5 |
Ice Season
Historical ice data from Minnesota DNR (5 observations).
| Earliest | Latest | |
|---|---|---|
| Ice-Out | 2017-03-23 (2017) | 2006-04-05 (2006) |
| Ice-In | 1993-11-22 (1993) | 1993-11-22 (1993) |
Most recent ice-out: 2017-03-23
Reservoir Info (USACE NID)
Riley Lake is a man-made reservoir impounded by the Lake Riley (completed 1958), built primarily for recreation on the Riley Creek; gravity-type dam, 9 ft tall and 20 ft long.
- Surface area
- 296 ac
- Normal storage
- 3,000 ac-ft
- Max storage
- 3,900 ac-ft
- Drainage area
- 8.3 sq mi
- Hazard class
- Undetermined
- Owner
- MNDNR
Source: USACE National Inventory of Dams, NID ID MN00411 · Operator website
EPA Impairment Status
Riley Lake is officially listed as impaired under Clean Water Act §303(d) in the 2024 EPA reporting cycle (IR category 5).
Causes of impairment
A Total Maximum Daily Load (TMDL) plan has been approved.
Source: EPA ATTAINS assessment unit MN10-0002-00 · Official waterbody report
County Ranking
Ranked #4 of 81 lakes in Hennepin County
Nearby Lakes in Hennepin County
Frequently asked questions about Riley Lake
What is the water quality grade for Riley Lake?
- Riley Lake in Hennepin County, Minnesota has a water quality grade of A (Excellent). Water clarity: 11.5 ft visibility. Phosphorus: 24 µg/L. Chlorophyll-a (algae): 6.5 µg/L. Maximum depth: 49 ft. Surface area: 296.21 acres.
Is Riley Lake safe to swim in?
- Excellent for swimming, crystal clear water with minimal algae. Riley Lake has a water quality grade of A (Excellent). Algae concentration (chlorophyll-a) is 6.5 µg/L. Always check local health department advisories before swimming.
What is the water temperature of Riley Lake?
- Riley Lake typically sits around 63°F at the surface in August, from 1,474 EPA Water Quality Portal field readings (2010–2025). That is a typical value for the month, not a live reading.
How deep is Riley Lake?
- Riley Lake has a maximum depth of 49 feet and an average depth of 21 feet. The lake covers 296.21 acres.
What fish are in Riley Lake?
- Fish species found in Riley Lake include black bullhead, black crappie, bluegill, brown bullhead, hybrid sunfish, largemouth bass, northern pike, pumpkinseed, walleye, yellow bullhead, yellow perch. Riley Lake is located in Hennepin County, Minnesota.
When does Riley Lake thaw?
- Riley Lake typically has ice-out around Apr 5.
Are there boat ramps on Riley Lake?
- Riley Lake has 1 documented boat landing in the USGS National Boat Ramps inventory. Named access points include Riley Lake. Public access is listed as yes.
Explore Riley Lake across LakeGrade
Depth, room, public access, and the state wake-sport rules
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Species activity outlook by water temperature and season
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Moderate nutrients, good water quality
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Where this data comes from
321 measurements from 2 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
MNPCA321 samples · 2020–2025
Analytical methods
- Field measurement/observation, generic method
- Phosphorus by Two Reagent Colorimetry
- Phosphorus by Colorimetry
- Analysis of Chlorophyll in Periphyton and Plankton
- 10200 H ~ Chlorophyll a-b-c Determination
Monitoring station identifiers (2)
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