Byllesby Lake
Dakota County, Minnesota1,368 acresView mapDirections
Minnesota PCA publishes the water-quality measurements for Byllesby Lake. Here is what has been measured.
- Hypereutrophic
- Impaired · Mercury
- 2 aquatic invasives
- 50 ft max depth
- Public access
- Limited data
Byllesby Lake in Dakota County, Minnesota has water-quality measurements published by Minnesota PCA, shown here as reported. 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.
Minnesota DNR's Targeted Survey on June 13, 2023 caught 2.12 walleye per gill net at Byllesby Lake. Length samples in the latest survey that recorded them ran 11–27 inches. DNR survey details →
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. 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. Methodology: how these readings are compared.
Byllesby Lake covers about 1,400 acres in Dakota County. It has 3 public boat landings, so a lakefront rental is not the only way to get a boat on the water. For a place on the water, look through cabin and lake-house rentals near Byllesby Lake on Vrbo. For a hotel or motel room, Booking.com and Expedia both search around the lake.
What Byllesby Lake is good for
From access and monitoring records, not editorial picks.
- Boat launch3 documented ramps
- Fishing19 species recorded
- Deep water50 ft surveyed max depth
- Big water1,368 acres
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. Byllesby Lake is listed impaired under Clean Water Act §303(d) (IR 4A) for mercury, nutrients (phosphorus, nitrogen). Check local advisories before you swim.
Whether Byllesby 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 Byllesby Lake
These are the measurements Minnesota PCA publishes for Byllesby 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 3 ft of visibility. Phosphorus 227 µg/L. Chlorophyll-a 40.7 µg/L. TSI 70.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | 3ft | Measured, not scored How deep a black-and-white disk stays visible from the surface. Higher is clearer. |
| Total phosphorus | 227µg/L | Poor GoodFairPoor |
| Chlorophyll-a (algae) | 40.7µg/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. | 70 | Hypereutrophic OligotrophicMesotrophicEutrophicHypereutrophic |
Very high nutrients, dense algae, poor clarity
Ask about Byllesby Lake
Answers come straight from the public measurements and survey records on this page.
Water Temperature
Byllesby Lake typically sits around 52°F at the surface in October. 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.
Column height runs from this lake’s coldest month (52°F) to its warmest (76°F).
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 →
Minnesota DNR's Targeted Survey on June 13, 2023 caught 2.12 walleye per gill net at Byllesby Lake. Length samples in the latest survey that recorded them ran 11–27 inches.
A DNR fisheries survey reports fish abundance and catch rates, not water quality. LakeQuality shows Byllesby Lake’s water-quality measurements separately, and the water-quality trend over 3 years of monitoring is declining. Catch rate is not a swim clearance and is not a weekly bite report.
DNR Fisheries Survey Summary
16 surveys on file from MN DNR Fisheries. Most recent: 2023-06-13 (Targeted Survey).
16 surveys on file · most recent 2023-06-13 (Targeted Survey)
| Species | Catch rate (CPUE) | Size | Avg weight |
|---|---|---|---|
| Common Carp | 40.31 | 22–30 in 2023-06-13 | 2.4 lb |
| Black Bullhead | 19.69 | 5–8 in 2023-06-13 | 0.31 lb |
| Largemouth Bass | 14.67 | 4–18 in 2019-06-03 | 0.86 lb |
| Golden Shiner | 13.17 | 0.53 lb | |
| Walleye | 10.04 | 11–27 in 2023-06-13 | 1.46 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.
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
Lake Details
Max depth
50 ft
Surface area
1,368 acres
Shoreline
13.9 mi
Littoral zone
71%
Share shallower than 15 ft
Public access
Yes
Listed by Minnesota PCA
Lake Size & Watershed
Watershed (drainage) area
1,100 sq mi
HydroLAKES / HydroSHEDS
Elevation
843 ft
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS).
Recreation & Access
- Lake Byllesby (Southeast)Public
- Lake Byllesby (West)Public
- Lake Byllesby (Northeast)Public
Named access points in the USGS National Boat Ramps inventory, within about 3 miles. More lakes with boat ramps
Stays via Stay22
Stays 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 readings cover nutrients and algae, not lodging. Cabins and rentals around Byllesby Lake are listed below.
Top-rated places to stay near Byllesby 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 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.
Water quality readings over time
3 seasons of samples on record (2022–2025). Calling a direction takes at least 4 years of the same measurement.
Water clarity
Worsening3 years
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
Designated uses not supporting: Fish consumption, Recreation.
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.
Nearby Lakes in Dakota County
Frequently asked questions about Byllesby Lake
Where is Byllesby Lake?
- Byllesby Lake is a lake in Dakota County, Minnesota. Its water-quality measurements are published by Minnesota PCA and shown on this page as reported.
What is the water quality of Byllesby Lake?
- Byllesby Lake in Dakota County, Minnesota has water-quality measurements published by Minnesota PCA, shown here as reported. 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?
- Nutrient and algae readings are not a swimming clearance. Byllesby Lake is listed impaired under Clean Water Act §303(d) (IR 4A) for mercury, nutrients (phosphorus, nitrogen). Check local advisories before you swim.
What is the water temperature of Byllesby Lake?
- Byllesby Lake typically sits around 52°F at the surface in October, 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.
What did the DNR fisheries survey find at Byllesby Lake?
- Minnesota DNR's Targeted Survey on June 13, 2023 caught 2.12 walleye per gill net at Byllesby Lake. Length samples in the latest survey that recorded them ran 11–27 inches. A DNR fisheries survey reports fish abundance and catch rates, not water quality. LakeQuality shows Byllesby Lake’s water-quality measurements separately, and the water-quality trend over 3 years of monitoring is declining. Catch rate is not a swim clearance and is not a weekly bite report.
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.
Can I fish at Byllesby Lake?
- Byllesby Lake has 3 documented boat landings 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 Byllesby Lake across LakeQuality
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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)
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
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