This Castle Rock Flowage area base map, while representing the best information currently available to the Wisconsin River Power Company (WRPCO), should not be relied upon entirely by those using flowage waters and land for fishing, boating, swimming, hiking and other recreational activities. Individuals must use extreme caution because of the size, complexity, and constantly changing conditions of Castle Rock Flowage. The information on the map is a composite of United States Coast and Geodetic Survey (USC&GS) data and underwater contour data provided by the University of Wisconsin-Stevens Point (UW-SP) and the Wisconsin Department of Natural Resources (DNR).
Persons desiring more information or wishing to report particular incidents or conditions observed on Castle Rock Flowage may contact a WRPCO representative at 1-800-53-WATCH.
The Castle Rock Flowage consists of 16,640 acres and is the fourth largest inland body of water in Wisconsin. It was built in the late 1940s for hydroelectric generation and flood control. The flowage is on Wisconsin's Central plain or Central Sand, the ancient bed of Glacial Lake Wisconsin that was a prehistoric one-million-acre body of water.
The Wisconsin River is the hardest working river in the nation. From its headwaters on the Wisconsin-Michigan border in Lac Vieux Desert, it falls more than 1,000 feet on its 500-mile journey through the state, before emptying into the Mississippi River at Prairie du Chien.
Since the Ice Age, the mighty river has scoured gorges and cut great rapids and waterfalls, whose roar has been replaced by the hum of turbines and waterwheels at 26 hydroelectric dams. The energy generated each year would supply the electrical needs of every home in Madison for a year.
The Wisconsin, long notorious for devastating floods, is now partially controlled by 21 reservoirs (flowages) on the river. Many reservoirs are lowered prior to spring runoff in anticipation of high water when spring breakup begins.
The Castle Rock Dam and the Petenwell Dam (its sister upriver) are unique, because they are built on sand and were the first such projects undertaken in the United States. The concrete dams are classified as "floating-type construction" with imbedded cutoff walls that penetrate deep into the glacial sands, permanently anchoring them.
Prior to construction of the Castle Rock Dam, the lake bed was farmland, prairie, and forested knolls and was bisected by the meandering Wisconsin River. As with most flowages, Castle Rock is relatively shallow and quickly becomes turbulent on windy days. Bottom conditions and depths vary considerably. Boaters are urged to become familiar with this map before any activity on the flowage.
Since flowage establishment, most of WRPCO's surrounding land has been open to the public for hunting, fishing, hiking, nature observation, skiing, and other recreational activities. Also, several 40-acre blocks have been dedicated as school forests. The flowage's namesake, Castle Rock, is downriver from the dam and is a local geological landmark.
The power company has opened selected portions of its east dike to public use for fishing, hiking, and nature observation, on a trial basis. Hunting and trapping are not permitted. The area offers good views of the flowage and some bank fishing. Located in Adams County in the Town of Quincy, this area stretches from Adams County Castle Rock Park south to the public access point near the Castle Rock Dam and Powerhouse.
Parking for the east dike is available at the Adams County Castle Rock Park or Castle Rock Dam areas. Absolutely no vehicular traffic is permitted on the dike system. Campfires and overnight camping are also prohibited.
Persons who have special interests in visiting closed portions of the dike system and related wildlife areas should contact WRPCO for more information.
The power company has cooperated with the Wisconsin DNR in establishing a trout fishery in portions of the Castle Rock ditch system and in erection of osprey nesting platforms and wood duck nests. The backwaters and sloughs immediately below Petenwell Dam, a favorite winter refuge for bald eagles, have been designated as a wildlife refuge by the power company. In cooperation with the DNR, the Federal Energy Regulatory Commission (FERC), and UW-SP, WRPCO has completed a management plan for this area. A walking trail through portions of the area is open to the public from May 1 to October 1.
Professional foresters manage forest land surrounding the Castle Rock Flowage for sustained timber production. More than 2,000 acres of marginal farmland have been forested, and over two million trees have been planted.
The flowage offers some of the Wisconsin River's best fishing. Locally known fishing "hot spots" include the railroad bridge crossing, the area near the Buckhorn Bridge, and the east bank below the dam. These areas provide abundant underwater structure and harbor good concentrations of fish.
The primary purpose of the Castle Rock Flowage is to store water that creates a water head (height) to produce electricity as it passes (drops) through the hydroturbines at the dam.
Flood control is another purpose. Flood control is accomplished by an annual drawdown that begins in February. The drawdown is governed by the amount of water in the snowcover in the state's northern section. The flowage is refilled as the snow melts, normally beginning in late March. By May 1, the flowage must be full and at normal summer levels. Between June 15 and February 1, the headwater elevation fluctuation is limited to a maximum of one foot.
The Castle Rock Dam is operated by the WRPCO under licenses from the FERC. The federal license provides control over flowage operations and requires that the company outline an overall land use and recreation plan that provides for full public utilization of the waters and land. The current license expires on December 7, 2031.
A flashing beacon is a warning that a flood gate is open. All boaters should always stay at least 500 feet upstream from the dam. For added safety, a restraining cable with orange floats and regulatory warning buoys have been installed, as shown on the above drawing. The cable is installed after spring breakup and is removed in late October. This cable spans the upstream powerhouse intake area and the gate section. Anchoring to the cable, except for emergencies, is prohibited.
Similar cable and floats have been installed just downstream from the turbine discharge area. These hydro units are remote controlled and can come on without warning. Safe boating procedures are a must, especially near dams!
Because Castle Rock is a flowage, it naturally becomes more shallow further upriver. The waters also conceal shallows in other unexpected areas, even long distances from shore. The northern portions of the Wisconsin River and Yellow River areas of the flowage, as well as the west shore south of the railroad bridge, also have shallow, stumpy areas. Therefore, proceed with caution.
Boaters may occasionally encounter floating debris from upriver or which broke loose from the shoreline. If the debris poses a water hazard, please mark it and notify a representative of the power company at 1-800-53-WATCH.