Byllesby Lake
Dakota County, MinnesotaHypereutrophic
Byllesby Lake earns an F: 220 µg/L of phosphorus and clarity at 3.0 ft signal heavy nutrient loading from the surrounding watershed. With clarity and phosphorus scored, the sub-grades cluster within a letter of each other, pointing to stable conditions rather than one specific stressor.
The hypereutrophic status — TSI 72 — reflects sustained heavy nutrient loading from the surrounding watershed and frequent algal pressure. At 50 ft of maximum depth, Byllesby Lake stratifies reliably through the summer — the hypolimnion stays cooler and clearer than the surface layer suggests. Byllesby Lake covers 1,368 acres alongside 13.9 miles of shoreline, large enough that conditions can vary meaningfully between bays. Byllesby Lake ranks 35 of 36 in Dakota County — at the lower end of the locally monitored distribution.
Byllesby Lake is on the Minnesota infested-waters list for zebra mussels — boaters should follow clean-drain-dry protocols when moving gear to or from the lake. Walleye are documented at Byllesby Lake, one of 19 fish species on record for the lake. A documented public access point at Byllesby Lake makes the lake usable for shore fishing, paddle craft, and trailered boats. Monitoring depth is thin here: the LakeGrade rubric is applied to a small number of sample years, and the grade will be revised as more data accumulates.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2024-09-29. Grade methodology: LakeGrade methodology.
Track Byllesby Lake
Subscribe for LakeQuality updates by email. No spam, unsubscribe anytime.
Swimming Safety
Avoid swimming, very poor water quality, potential algae toxins
Water Quality Grade: F, Very Poor
Very murky, less than 3 ft of visibility. Phosphorus level: 220 µg/L. Trophic State Index: 72.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 3 ft | F |
| Phosphorus | 220 µg/L | F |
| Chlorophyll-a (Algae) | No data | |
| Trophic State Index (TSI) | 72 | Hypereutrophic |
Very high nutrients, dense algae, poor clarity
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | 50 ft |
| Surface Area | 1.4K acres |
| Shoreline Length | 13.9 mi |
| Littoral Zone | 71% |
| Public Access | Yes |
Fish Species
Click a species to see all Minnesota and Wisconsin lakes where it is found.
→ Best fishing times for Byllesby Lake (14-day solunar calendar)
→ Is it safe to eat fish from Byllesby Lake? (mercury & PFAS guide)
→ Byllesby Lake fishing regulations (limits, seasons, special rules)
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 Trend: ↓ Declining
Based on 2 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↓ Declining | -0.245 m/yr | 2 |
Location
County Ranking
Ranked #35 of 36 lakes in Dakota County
Nearby Lakes in Dakota County
More Minnesota Lake Rankings
State Parks Near Byllesby Lake
Other Grade F Lakes in Minnesota
Compare Byllesby Lake With Nearby Lakes
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.
- —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
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
Data Sources
Water quality data from the EPA Water Quality Portal
Impairment status from EPA ATTAINS 303(d) database
Grading methodology based on Metropolitan Council standards
Lake details from Minnesota DNR LakeFinder
Most recent sample: 2024-09-29
Monitoring stations: 1