Rock Lake (Tyranena Park Lake Access), Lower Crawfish River Watershed (UR02)
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Rock Lake (Tyranena Park Lake Access), Lower Crawfish River Watershed (UR02)
Rock Lake (Tyranena Park Lake Access) (830700)
0.04 Miles
0 - 0.04
Natural Community
Deep Lowland
Year Last Monitored
2025
Unknown
 
Jefferson
Trout Water 
No
Outstanding or Exceptional 
No
Impaired Water 
No

Fish and Aquatic Life

Current Use
Supported Aquatic Life
Attainable Use
Default FAL
Designated Use
Default FAL

Overview

Rock Lake is a borderline high-quality mesotrophic lake. It has been the focus of long-term trend monitoring from 1986 to 1998. In 1999 and 2000, DNR baseline monitoring was conducted on Rock Lake. Ongoing monitoring indicates good water quality, but lake fertility is increasing (WDNR, 1994). This increased fertility may lead to more algae blooms. The lake was chemically treated in the past to control excessive aquatic plant growth, but this management practice has decreased due to potential harm to fish habitat. The lake has a diverse sport fishery supporting both smallmouth and largemouth bass, walleye, northern pike and panfish. A fish consumption advisory exists for walleye; past fish tissue monitoring has found elevated levels of mercury in walleye. The source of the metal is unknown (WDNR, 1994); it may originate from natural sources.

Polluted runoff is the greatest threat to Rock Lake. Residential development along the shoreline and backlot development adjacent to the lake have recently accelerated. Agricultural runoff carrying excess nutrients to the lake also contributes to water quality concerns.

A lake planning grant was awarded to the Rock Lake Improvement Association to develop an overall lake management plan. Other lake planning grants may be needed to address other issues. Rock Lake is monitored through WDNR's self-help monitoring programs. The least darter, a fish on the state's watch list, has been observed in Rock Lake (Fago,1982).

In 1999, the Rock Lake was designated by the DNR Nonpoint Source Pollution Project as a Priority Lakes Nonpoint Source Pollution Control Project. A plan was written and the implementation process in underway. The project will end in 2004.


In 2002, the county acquired 89 acres of wetlands, uplands, and woodlands on the western shore of Rock Lake. The land was purchased for development of a county park.
Also in 2002, Jefferson County obtained a DNR Lakes Planning Grant to conduct a lake classification project in the county. A Citizens Advisory Group was formed of diverse stakeholders in the county to develop a plan to increase protection of the lakes in the county.

Date  2002

Author   Aquatic Biologist

Historical Description

Source: 1968, Surface Water Resources of Jefferson County Rock Lake, T7N, R13E, Section 10, 11, 14, 15

A large compound depression in the ground moraine, which has a shoreline greatly altered by the construction in 1865 of a dam with about a 10 foot head. The southern basin of the lake is largely the result of impoundment and is sometimes referred to as Marsh Lake. The fishery consists of northern pike, walleye, yellow perch, largemouth and smallmouth bass and most panfishes. Carp are present but not in problem proportions. The lake is quite fertile and generally clear. There is a 3.1 acre city park and a 15.5 acre county park on its banks. The county park has an improved boat launching site with adequate parking. About 1,700 acres of wetland lie within this watershed and encompass Mud Lake and Bean Lake to the south. The west shore is somewhat marshy and has been the object of some dredging and shore alteration in the past. Large numbers of coots are common; mallards, teal and geese also frequent the lake especially the south lobe (Marsh Lake). The city of Lake Mills borders more than one-third of the shoreline.

Surface Acres = 1,371.0, S.D.F. = 1.43, Maximum Depth = 56 feet

Date  1968

Author   Surface Water Inventory Of Wisconsin

Natural communities (stream and lake natural communities) represent model results that use predicted flow and temperature based on landscape features and related assumptions. Ranges of flow and temperature associated with specific aquatic life communities (fish, macroinvertebrates) help biologists identify appropriate resource management goals. Wisconsin Natural Communities.
This is the most recent date of monitoring data stored in SWIMS. Additional surveys for fish and habitat may be available subsequent to this date.
Trout Waters are represented by Class I, Class II or Class III waters. These classes have specific ecological characteristics and management actions associated with them. For more information regarding Trout Classifications, see the Fisheries Trout Class Webpages.
Wisconsin has designated many of the state's highest quality waters as Outstanding Resource Waters (ORWs) or Exceptional Resource Waters (ERWs). Waters designated as ORW or ERW are surface waters which provide outstanding recreational opportunities, support valuable fisheries and wildlife habitat, have good water quality, and are not significantly impacted by human activities. ORW and ERW status identifies waters that the State of Wisconsin has determined warrant additional protection from the effects of pollution. These designations are intended to meet federal Clean Water Act obligations requiring Wisconsin to adopt an 'antidegradation' policy that is designed to prevent any lowering of water quality - especially in those waters having significant ecological or cultural value.
A water is polluted or 'impaired' if it does not support full use by humans, wildlife, fish and other aquatic life and it is shown that one or more of the pollutant criteria are not met.
The use the water currently supports. This is not a designation or classification; it is based on the current condition of the water. Information in this column is not designed for, and should not be used for, regulatory purposes.
Waters that support fish and aquatic life communities (healthy biological communities).
The use that the investigator believes the water could achieve through managing "controllable" sources. Beaver dams, hydroelectric dams, low gradient streams, and naturally occurring low flows are generally not considered controllable. The attainable use may be the same as the current use or it may be higher.
Fish and Aquatic Life - Default Waters do not have a specific use designation subcategory but are considered fishable, swimmable waters.
This is the water classification legally recognized by NR102 and NR104, Wis. Adm. Code. The classification determines water quality criteria and effluent limits. Waters obtain designated uses through classification procedures.
Fish and Aquatic Life - Default Waters do not have a specific use designation subcategory but are considered fishable, swimmable waters.