Byllesby Lake
Byllesby Lake in Dakota County, Minnesota has a water quality grade of F (Algae-prone). Water clarity: 3 ft visibility. Phosphorus: 227 µg/L. Chlorophyll-a (algae): 40.7 µg/L. Maximum depth: 50 ft. Surface area: 1368.31 acres.
- Clarity
- 3 ft
- Typical in August
- 76°F
- Max depth
- 50 ft
- Area
- 1,368 acres
- Type
- Hypereutrophic
- Trend
- ↓ Declining
- Public access
- Yes
Grade F measures nutrients and algae, not whether this is a good place for a cabin trip. Cabins and rentals near Byllesby Lake →
Next lake in Dakota County
Free interactive depth-contour map of Byllesby Lake, reaching a maximum surveyed depth of 50 ft. Toggle Depth contours to overlay the bathymetric survey lines. Contour data from Minnesota DNR.
Byllesby Lake is a 1,368-acre highly nutrient-loaded hypereutrophic lake in Dakota County, Minnesota with a maximum depth of 50 feet. Water quality is graded F based on 2 sampling years through 2025. Overall water quality is declining over recent sampling years. The lake supports 19 documented fish species including bigmouth buffalo, black bullhead, and black crappie. Public access is available with 3 public boat landings. Compared to the 44 other monitored lakes in Dakota County, Byllesby Lake ranks #41 for water quality.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2025-10-03. Grade methodology: LakeGrade methodology.
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Swimming Safety
Grade onlyLimited data
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 3 ft of visibility. Phosphorus level: 227 µg/L. Chlorophyll-a: 40.7 µg/L. Trophic State Index: 70.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 3 ft | Not graded |
| Phosphorus | 227 µg/L | Poor |
| Chlorophyll-a (Algae) | 40.7 µg/L | Poor |
| Trophic State Index (TSI) | 70 | Hypereutrophic |
Very high nutrients, dense algae, poor clarity
Where to stay near Byllesby Lake
Compare lakeside cabins, hotels, and vacation rentals near Byllesby Lake in Dakota 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 Byllesby Lake are listed below.
Top-rated places to stay near Byllesby Lake
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Planning a whole trip? See where to stay at Minnesota’s top lakes →
Water Temperature
Byllesby Lake typically sits around 76°F at the surface in August. Summer average is about 74°F. Usually warmest in Jul (about 76°F) and coldest in Oct (about 52°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 97 field readings (2019–2025) via the EPA Water Quality Portal. See the full Byllesby Lake water temperature breakdown →
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | 50 ft |
| Surface Area | 1,368 acres |
| Shoreline Length | 13.9 mi |
| Littoral Zone | 71% |
| Public Access | Yes |
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS).
Recreation & Access
- Lake Byllesby (Southeast)Public
- Lake Byllesby (West)Public
- Lake Byllesby (Northeast)Public
Fish Species
Click a species to see every graded lake where it is documented.
Fishing Byllesby 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
16 surveys on file from MN DNR Fisheries. Most recent: 2023-06-13 (Targeted Survey).
Top Species by Catch Rate
| Species | Avg CPUE | Avg Weight |
|---|---|---|
| Common Carp | 40.31 | 2.4 lb |
| Black Bullhead | 19.69 | 0.31 lb |
| Largemouth Bass | 14.67 | 0.86 lb |
| GOS | 13.17 | 0.53 lb |
| CRP | 12.71 | 1.5 lb |
| Walleye | 10.04 | 1.46 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.
Common Carp
Black Bullhead
Largemouth Bass
Walleye
From the 2023-06-13 survey
Lake Byllesby is located on the Goodhue and Dakota county line near the town of Cannon Falls. It is a 1,435-acre run of the river reservoir on the Cannon River created by a hydroelectric dam. Lake Byllesby has three public access, two on the lower end of the lake and one on the upper end. A fisheries survey consisting…
DNR Reports & Resources
Minnesota DNR LakeFinder publishes lake survey, fish stocking, water access, and aquatic plant data for Byllesby Lake. 3 reports on file.
These links open on the official state DNR websites (Wisconsin DNR survey PDFs · Minnesota DNR LakeFinder).
- —Fisheries Lake Survey — ByllesbyFisheries Lake Survey · MN DNR LakeFinder
- —Fish Stocking History — ByllesbyFish Stocking History · MN DNR LakeFinder
- —Public Water Access Sites — ByllesbyPublic Water Access Sites · MN DNR LakeFinder
Water Quality Trend: ↓ Declining
Based on 3 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↓ Declining | -0.175 m/yr | 3 |
Reservoir Info (USACE NID)
Byllesby Lake is a man-made reservoir impounded by the Lake Byllesby (completed 1911), built primarily for hydroelectric on the Cannon River; buttress-type dam, 75 ft tall and 2,870 ft long.
- Surface area
- 1,430 ac
- Normal storage
- 18,500 ac-ft
- Max storage
- 24,000 ac-ft
- Drainage area
- 1,160 sq mi
- Hazard class
- High
- Owner
- Dakota And Goodhue Counties
All listed purposes: Hydroelectric;Recreation.
Source: USACE National Inventory of Dams, NID ID MN00514 · Operator website
EPA Impairment Status
Byllesby 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 MN19-0006-00 · Official waterbody report
Regulated Pollution Sources Nearby
1 EPA-permitted facility operate within about 5 miles of Byllesby Lake under Clean Water Act (NPDES) discharge permits. 1 facility has a reported Clean Water Act violation in the past three years.
- Cannon Falls WwtpCannon Falls · 4.2 mi away · NPDES MN0022993Recent violation
Facilities permitted to discharge under the Clean Water Act within ~5 miles; proximity does not by itself mean a facility affects this lake. Source: EPA ECHO (ICIS-NPDES), as of 2026-07.
County Ranking
Ranked #41 of 45 lakes in Dakota County
Nearby Lakes in Dakota County
Frequently asked questions about Byllesby Lake
What is the water quality grade for Byllesby Lake?
- Byllesby Lake in Dakota County, Minnesota has a water quality grade of F (Algae-prone). Water clarity: 3 ft visibility. Phosphorus: 227 µg/L. Chlorophyll-a (algae): 40.7 µg/L. Maximum depth: 50 ft. Surface area: 1368.31 acres.
Is Byllesby 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. Byllesby Lake has a water quality grade of F (Algae-prone). Algae concentration (chlorophyll-a) is 40.7 µg/L. Always check local health department advisories before swimming.
What is the water temperature of Byllesby Lake?
- Byllesby Lake typically sits around 76°F at the surface in August, from 97 EPA Water Quality Portal field readings (2019–2025). That is a typical value for the month, not a live reading.
How deep is Byllesby Lake?
- Byllesby Lake has a maximum depth of 50 feet. The lake covers 1368.31 acres.
What fish are in Byllesby Lake?
- Fish species found in Byllesby Lake include bigmouth buffalo, black bullhead, black crappie, bluegill, channel catfish, common carp, flathead catfish, freshwater drum, golden redhorse, largemouth bass, northern pike, quillback, shorthead redhorse, smallmouth bass, walleye, white bass, white crappie, white sucker, yellow perch. Byllesby Lake is located in Dakota County, Minnesota.
Are there boat ramps on Byllesby Lake?
- Byllesby Lake has 3 documented boat landings in the USGS National Boat Ramps inventory. Named access points include Lake Byllesby (Southeast), Lake Byllesby (West), Lake Byllesby (Northeast). Public access is listed as yes.
Explore Byllesby 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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Where this data comes from
36 measurements from 1 monitoring station, 2022–2025. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Minnesota Pollution Control Agency - Ambient Surface Water
MNPCA36 samples · 2022–2025
Analytical methods
- Field measurement/observation, generic method
- Phosphorus by Colorimetry
- 10200 H ~ Chlorophyll a-b-c Determination
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
Regulated discharger data from EPA ECHO (ICIS-NPDES)
Lake size & watershed from HydroLAKES (HydroSHEDS)
Lake details from Minnesota DNR LakeFinder
Named boat-access points from the USGS National Boat Ramps inventory