Nepco Lake
Wood County, WisconsinMesotrophic
Nepco Lake earns an A — water clarity, phosphorus, and chlorophyll-a all rate among the best monitored waters in Wood County. Clarity, phosphorus, and chlorophyll-a all rate similarly, so there is no obvious single lever to pull on watershed management.
The lake sits in the mesotrophic zone — the band where most well-managed Wisconsin lakes fall. A maximum depth of 29 ft puts Nepco Lake in the middle of Wisconsin's depth distribution. Nepco Lake covers 496 acres alongside partial shoreline records — a mid-sized water that supports a working fishery without being so large that conditions diverge between basins. Nepco Lake ranks 1 of 4 in Wood County, putting it in the upper tier of locally monitored lakes.
Zebra mussel presence at Nepco Lake means the lake's clarity numbers carry an asterisk — filtered water is not the same as nutrient-poor water. The fishery includes walleye alongside the lake's other 6 documented species — a notable draw for Wisconsin anglers. A documented public access point at Nepco Lake makes the lake usable for shore fishing, paddle craft, and trailered boats. 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 2025-09-30. Grade methodology: LakeGrade methodology.
Watch Nepco Lake water quality
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Swimming Safety
Excellent for swimming, crystal clear water with minimal algae
Water Quality Grade: A, Excellent
Good clarity, visible to about 11 ft. Phosphorus level: 10.9 µg/L. Trophic State Index: 41.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 11 ft | B |
| Phosphorus | 10.9 µg/L | A |
| Chlorophyll-a (Algae) | No data | |
| Trophic State Index (TSI) | 41 | Mesotrophic |
Moderate nutrients, good water quality
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | 29 ft |
| Surface Area | 496 acres |
| Public Access | Yes |
Fish Species
Click a species to see every graded lake where it is documented.
→ Best fishing times for Nepco Lake (14-day solunar calendar)
→ Is it safe to eat fish from Nepco Lake? (mercury & PFAS guide)
→ Nepco 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: → Stable
Based on 4 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↓ Declining | -0.775 m/yr | 4 |
| Phosphorus | ↑ Improving | -1.75 µg/L/yr | 3 |
Recreation & Access
Location
County Ranking
Ranked #1 of 4 lakes in Wood County
Nearby Lakes in Wood County
More Wisconsin Lake Rankings
State Parks Near Nepco Lake
Other Grade A Lakes in Wisconsin
Washington County · Clarity: 11.8 ft
Washington County · Clarity: 12.6 ft
Walworth County · Clarity: 11 ft
Waukesha County · Clarity: 11.3 ft
Walworth County · Clarity: 20.2 ft
Kenosha County · Clarity: 10 ft
Mesotrophic Lakes in Wisconsin
WI DNR Lake Profile
Authoritative data from the Wisconsin DNR LakePages. Monitored by volunteers since 2013. 1 station on file (most recent sample 2025).
Fish Species (DNR-rated)
Reservoir Info (USACE NID)
Nepco Lake is a man-made reservoir impounded by the Four Mile Creek (completed 1926), built primarily for water supply on the FOURMILE CREEK & BLOODY RUN; gravity-type dam, 33 ft tall and 2,084 ft long.
- Surface area
- 494 ac
- Normal storage
- 4,748 ac-ft
- Max storage
- 6,000 ac-ft
- Drainage area
- 29 sq mi
- Hazard class
- Low
- Owner
- Domtar Wisconsin Dam Corp.
All listed purposes: Water Supply;Recreation;Hydroelectric.
Source: USACE National Inventory of Dams, NID ID WI00032 · Operator website
Data Sources
Water quality data from the EPA Water Quality Portal
Grading methodology based on Metropolitan Council standards
Fish and recreation data from Wisconsin DNR Lakes
Public boat-access points from the USGS National Boat Ramps inventory
Most recent sample: 2025-09-30
Monitoring stations: 1
Where to stay near Nepco Lake
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