Rock River Lake
Rock County, Wisconsin548 acresView mapDirections
Wisconsin DNR publishes the water-quality measurements for Rock River Lake. Here is what has been measured.
- Public access
- Limited data
Rock River Lake in Rock County, Wisconsin has water-quality measurements published by Wisconsin DNR, shown here as reported. Water clarity: 21 ft visibility. Surface area: 548 acres.
Rock River Lake is a 548-acre lake in Rock County, Wisconsin. Limited fish-species data available. Public access is available with 1 public boat landing.
Source: EPA Water Quality Portal sampling records, Wisconsin DNR Surface Water, last sampled 2021-07-06. Methodology: how these readings are compared.
What Rock River Lake is good for
From access and monitoring records, not editorial picks.
- Clear water21 ft of visibility
- Boat launch1 documented ramp
Swimming conditions
No readingBacteria tested: exceedances
Based on E. coli testing, Rock River Lake occasionally exceeded the EPA safe-swimming threshold (235 MPN/100mL) — on 7.9% of 164 samples across 9 seasons.
This is a historical summary of past testing, not a current condition — bacteria levels change quickly, especially after rain. Always check Wisconsin’s current beach and health-department advisories before swimming.
Whether Rock River Lake is safe to swim in today is a call for the Wisconsin Department of Natural Resources and the county health department, who post current advisories. LakeQuality does not issue swimming clearances.
Water quality measurements for Rock River Lake
These are the measurements Wisconsin DNR publishes for Rock River Lake, shown as reported. The condition class beside each reading is the EPA National Lakes Assessment class for this lake’s ecoregion.
Crystal clear, you can see 21 ft down. TSI 33.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | 21ft | Measured, not scored How deep a black-and-white disk stays visible from the surface. Higher is clearer. |
| Total phosphorus | No reading The nutrient that most limits algae growth in freshwater. More phosphorus, more algae potential. | |
| Chlorophyll-a (algae) | No reading The green pigment in algae — a direct measure of how much algae is in the water. | |
| Trophic state (TSI)Carlson's 0–100 index of how much algae a lake can support, from clarity, phosphorus and chlorophyll-a. | 33 | Oligotrophic OligotrophicMesotrophicEutrophicHypereutrophic |
Low nutrients, clear water. No reading is a swimming clearance.
Ask about Rock River Lake
Answers come straight from the public measurements and survey records on this page.
Water Temperature
Rock River Lake typically sits around 75°F at the surface in August. Summer average is about 75°F. Usually warmest in Jul (about 77°F) and coldest in May (about 66°F). These are typical values by month — not a live reading.
Column height runs from this lake’s coldest month (66°F) to its warmest (77°F).
Typical surface water temperature by month, from 30 field readings (2024–2026) via the EPA Water Quality Portal. See the full Rock River Lake water temperature breakdown →
DNR Reports & Resources
Wisconsin DNR Fisheries scientists publish multi-year survey reports for Rock River Lake covering fish populations, stocking, water quality, and management. 1 report on file.
These links open on the official state DNR websites (Wisconsin DNR survey PDFs · Minnesota DNR LakeFinder).
- 2025Rock River fall shocking survey, 2025Fisheries Survey · WI DNR · 2025 (PDF)
Lake Details
Surface area
548 acres
Public access
Yes
Listed by Wisconsin DNR
No bathymetric survey has been published for Rock River Lake, so its depth is not documented here.
Recreation & Access
- Traxler ParkPublic
Named access points in the USGS National Boat Ramps inventory, within about 3 miles. More lakes with boat ramps
Stays via Stay22
Stays near Rock River Lake
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Top-rated places to stay near Rock River Lake
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Fishing Rock River Lake
Reservoir Info (USACE NID)
Rock River Lake is a man-made reservoir impounded by the Central (completed 1927), built primarily for hydroelectric on the Rock River; timber crib-type dam, 8 ft tall and 325 ft long.
- Surface area
- 548 ac
- Normal storage
- 3,675 ac-ft
- Drainage area
- 3,205 sq mi
- Hazard class
- Low
All listed purposes: Hydroelectric;Recreation.
Source: USACE National Inventory of Dams, NID ID WI00790 · Operator website · Matched by proximity (0.7 km)
Regulated Pollution Sources Nearby
3 EPA-permitted facilities operate within about 5 miles of Rock River Lake under Clean Water Act (NPDES) discharge permits, including 1 classified by the EPA as major discharger. 1 facility has a reported Clean Water Act violation in the past three years.
- Janesville Wastewater UtilityJanesville · 4 mi away · NPDES WI0030350MajorRecent violation
- General Motors Corp/Truck AndJanesville · 1.8 mi away · NPDES WI0001945
- Seneca Foods Corp Janesville La Prairie PlantLa Prairie · 3 mi away · NPDES WI0050687
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 Rock County
Frequently asked questions about Rock River Lake
Where is Rock River Lake?
- Rock River Lake is a lake in Rock County, Wisconsin. Its water-quality measurements are published by Wisconsin DNR and shown on this page as reported.
What is the water quality of Rock River Lake?
- Rock River Lake in Rock County, Wisconsin has water-quality measurements published by Wisconsin DNR, shown here as reported. Water clarity: 21 ft visibility. Surface area: 548 acres.
Is Rock River Lake safe to swim in?
- Based on E. coli testing, Rock River Lake occasionally exceeded the EPA safe-swimming threshold (235 MPN/100mL) — on 7.9% of 164 samples across 9 seasons. That is a historical summary of past bacteria testing, not a current reading and not a swimming clearance. Bacteria levels can spike quickly after heavy rain, so whether Rock River Lake is safe to swim in today is a call for Wisconsin's water agency and the county health department; check their current beach advisories before you swim.
What is the water temperature of Rock River Lake?
- Rock River Lake typically sits around 75°F at the surface in August, from 30 EPA Water Quality Portal field readings (2024–2026). That is a typical value for the month, not a live reading.
Are there boat ramps on Rock River Lake?
- Rock River Lake has 1 documented boat landing in the USGS National Boat Ramps inventory. Named access points include Traxler Park. Public access is listed as yes.
Can I fish at Rock River Lake?
- Rock River Lake has 1 documented boat landing in the USGS National Boat Ramps inventory. Seasons, size and bag limits, and whether you need a license are set by Wisconsin's fish and wildlife agency, so check its current regulations before you go.
Explore Rock River Lake across LakeQuality
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Fish species and best lakes in Rock County
Species activity outlook by water temperature and season
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Where this data comes from
1 measurement from 1 monitoring station, 2021. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Wisconsin Department of Natural Resources
WIDNR_WQX1 sample · 2021
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
Regulated discharger data from EPA ECHO (ICIS-NPDES)
Fish and recreation data from Wisconsin DNR Lakes
Named boat-access points from the USGS National Boat Ramps inventory