Flynn Lake
Bayfield County, WisconsinLimited DataMesotrophic
Flynn Lake earns a C — middle-of-the-pack water quality, with one or two parameters dragging the average down from a stronger grade.
A TSI near 45 places Flynn Lake in the mesotrophic band — moderate productivity, with seasonal swings between clearer spring water and richer late-summer conditions. A maximum depth of just 9 ft means sediment-bound phosphorus releases back into the water column whenever wind stirs the bottom — a classic shallow-lake dynamic. At 30 acres, Flynn Lake sits below the Wisconsin median: a small water where shoreline activity has an outsized effect on water quality. Flynn Lake ranks 47 of 52 in Bayfield County — at the lower end of the locally monitored distribution.
Eurasian watermilfoil has been documented at Flynn Lake, requiring shoreline management to keep dense mats from crowding native vegetation. Walleye are documented at Flynn Lake, one of 6 fish species on record for the lake. The grade is based on limited monitoring — fewer than three independent measurement years contribute, so future updates may shift the letter.
Source: EPA Water Quality Portal sampling records, Wisconsin DNR Surface Water, last sampled 2023-06-01. Grade methodology: LakeGrade methodology.
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Swimming Safety
Generally safe for swimming, moderate water quality
Water Quality Grade: C, Fair
Moderate clarity, visible to about 9 ft. Trophic State Index: 45.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 9 ft | C |
| Phosphorus | No data | |
| Chlorophyll-a (Algae) | No data | |
| Trophic State Index (TSI) | 45 | Mesotrophic |
Moderate nutrients, good water quality
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | 9 ft |
| Surface Area | 30 acres |
Fish Species
Click a species to see all Wisconsin and Minnesota lakes where it is found.
→ Best fishing times for Flynn Lake (14-day solunar calendar)
→ Is it safe to eat fish from Flynn Lake? (mercury & PFAS guide)
→ Flynn 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: ↑ Improving
Based on 6 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↑ Improving | +0.825 m/yr | 5 |
| Phosphorus | ↑ Improving | -0.79 µg/L/yr | 6 |
Location
County Ranking
Ranked #47 of 52 lakes in Bayfield County
Cleaner Lakes Within 30 Miles
Flynn Lake holds Grade C. 2 nearby lakes hold higher grades.
Nearby Lakes in Bayfield County
More Wisconsin Lake Rankings
Other Grade C Lakes in Wisconsin
Mesotrophic Lakes in Wisconsin
WI DNR Lake Profile
Authoritative data from the Wisconsin DNR LakePages. 2 stations on file (most recent sample 2023).
Fish Species (DNR-rated)
Reservoir Info (USACE NID)
Flynn Lake is a man-made reservoir impounded by the Murrays (completed 1941), built primarily for recreation on the EAST FORK WHITE; gravity-type dam, 13 ft tall and 34 ft long.
- Surface area
- 650 ac
- Normal storage
- 19,960 ac-ft
- Max storage
- 22,000 ac-ft
- Drainage area
- 13 sq mi
- Hazard class
- Low
- Owner
- Bayfield County
Source: USACE National Inventory of Dams, NID ID WI00103 · Operator website · Matched by proximity (0.25 km)
Data Sources
Water quality data from the EPA Water Quality Portal
Grading methodology based on Metropolitan Council standards
Most recent sample: 2023-06-01
Monitoring stations: 1