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Lisa Helmuth
Water Quality Bureau

Lower Rock River surface water quality report

Basinwide issues

The Lower Rock River in south central Wisconsin extends 48 miles from Fort Atkinson to the Illinois-Wisconsin border at Beloit. A large, low velocity, warmwater river, it is classified as warmwater sport fishery. The main stem only partially supports its uses due to both urban and rural sources of polluted runoff, hydrologic modifications throughout its entire basin and, to a lesser degree, industrial and municipal point sources.

The river is often turbid from suspended solids and excess nutrients, algae and phytoplankton. A good fishery of walleye, catfish, panfish and northern pike exists between Fort Atkinson and Lake Koshkonong. Below Lake Koshkonong the fishery changes to crappie, northern pike, channel catfish, walleye and largemouth and smallmouth bass. There is a particularly good bass population between Janesville and Beloit.

Water quality data from monitoring stations on the Rock at Indianford and Afton have been collected since 1961. The data indicates solids and phosphorus are moderately high, as is expected in this type of river. All parameters evaluated have essentially the same concentrations at both stations, indicating no major extra input of nutrients or solids from the Yahara River and its associated watersheds. Except for dissolved oxygen, the data over the period of record shows a decreasing trend in concentrations, which may be due to improved wastewater treatment and land use management practices. The slightly lower dissolved oxygen concentrations at the Indianford station may be due to the eutrophic conditions of Lake Koshkonong. The minor decrease in dissolved oxygen over the 10-year period is difficult to explain, but it is important to note that all but one measurement is well above the water quality standard for dissolved oxygen of 5 milligrams per liter. The super-saturated dissolved oxygen concentrations do, however, indicate high photosynthetic activity and extreme diel (24-hour) fluctuations in dissolved oxygen.

The U.S. Army Corps of Engineers (COE) predicts water quality problems for a reach of the Rock River near Janesville by the year 2020. COE estimates water quality problems at Madison and Janesville will probably require intensive waste treatment beyond commonly accepted levels.

Analysis of 1991 data in the Lower Rock River main stem, below Fort Atkinson to the Illinois border, continues to show the presence of PCBs based on measurable concentrations in carp and large catfish. Lake Koshkonong shows low/undetectable concentrations in a 1991 whole fish carp sample and game species below detection. Wisconsin DNR needs to continue sampling whole-fish carp and fillets from catfish from the Rock River below Indianford and Janesville.

Shoreline development

Increasing development of lake, river and stream shorelines throughout the basin threatens the integrity of waterbodies and is a priority water quality issue in the basin. The Rock River basin is undergoing dramatic shoreline development throughout its entire main stem section and all tributaries, major and minor. Lakes, especially, are being developed. This has precipitated the manipulation of water levels of surface and groundwater in some areas of the Bark River watershed to maintain high quality water resources despite intensified development and the placement of septic systems near the lakeshore. Shoreline development dramatically alters the functional values of river and/or lake system and can cause major morphological and hydrological alterations to that system. Intense development has also occurred along a corridor starting north of the city of Janesville down through South Beloit and continuing past the city of Rockford in Illinois. The entire main stem of the Rock River also receives heavy boating pressure, which contributes to shoreline erosion.

City of Beloit

The southwestern portion of the city of Beloit is located at the mouth of this watershed. In the past the city experienced flooding on the west side and has recently funded the installation of a stormwater detention wetland system to abate this problem (Botts).

Recently, the city and town of Beloit and other surrounding towns have updated the Beloit Sewer Service Area Plan. This plan provides a guideline for locating sewered development for the next 20 years. Population projections used in the update indicated that while residential growth would be minimal and perhaps declining during the time period, land was allocated to commercial and industrial development along I-90 to attract new business and spur residential growth, particularly in the Turtle Creek watershed.

City of Janesville

The city of Janesville is a medium-to-large-sized urban center located along the main stem of the Rock River. Portions of the city fall in the Blackhawk Creek watershed (LR02), the Bass Creek watershed (LR03) and the Marsh Creek watershed (LR03). About 56,000 people live in the city, a number that grew by 7.5 percent from 1990 to 1995. A 1989 projection for population in the year 1995 was 59,645--3,000 above the current population estimate (RCPDA). A 1993 population analysis by the city of Janesville estimates 57,600 city residents by the year 2000 and 62,900 by the year 2010 at a growth rate of about 1 percent per year. Like many other metropolitan area, Janesville is experiencing migration from the city to the suburbs and outlying rural areas. Densities in the city have gradually decreased as more land has been annexed and the population has grown. The city is now in the process of updating its sewer service area plan to reflect shifts in urban/suburban growth.


  1. The Lower Rock River basin Team should conduct fish carp and catfish fillet sampling and monitor sediments for PCBs and heavy metals, in the Rock River above the dams at Indianford, Janesville and Fort Atkinson (type b).
  2. The Lower Rock River basin Team, with the Federal Energy Regulatory Commission (FERC) and Wisconsin Power & Light, should follow up on water resource recommendations from the FERC relicensing study on the effects of hydropower generation on water quality and fishery habitat in the Rock River System (type b).
  3. The cities of Fort Atkinson, Janesville and Beloit and Rock and Jefferson counties, should adopt and enforce construction site erosion control ordinances to reduce sediment entering the Rock River System (type c).
  4. The cities of Janesville, Fort Atkinson and Beloit should develop comprehensive stormwater management plans that integrate previous planning efforts (master plans, sewer service area plans, etc.) and that focus on reducing toxic, nutrient and sediment-laden runoff entering the Rock River system (type c).
  5. The Lower Rock River basin Team, as part of the Wisconsin DNR's Land Use Initiative, should analyze and support recommendations in the Department's June, 1995 document, Common Ground and recommendations forwarded in the State of Wisconsin's Planning Wisconsin: Report of the State Interagency Land Use Council, published in July, 1996, where applicable in the Lower Rock River basin (type c).
  6. Rock County should consider developing no-wake speed zones for portions of the Rock River, particularly areas adjacent or upstream from heavily eroding shorelines (type c).
  7. Rock County and the cities of Beloit and Janesville should take advantage of federal, state and private funding opportunities to acquire additional public access and lands along the Rock River (type c).
  8. The town and the city of Beloit should incorporate all environmentally sensitive areas into their open space and recreational use plans as preservation areas to encourage compliance with protection of these areas as is required in NR 121 (type c).
Last revised: Thursday December 10 2015