Rock Lake dam and water levels

Low levels in Rock Lake have caused significant concerns among Rock Lake users. Putting aside for a moment that we all know Mother Nature has a significant impact on lake Levels, below is background information and updates regarding efforts to ensure Rock Lake levels are maintained at appropriate levels.

Rock Lake levels are controlled in part by the Rock Lake Dam, which is operated by the City of Lake Mills. The Dam was constructed in 2018 and operates automatically to meet proscribed water levels.

The Wisconsin Department of Natural Resources (DNR) has regulatory authority over the dam (as well as many other dams in Wisconsin) and has issued an order specifying the levels at which Rock Lake is to be maintained throughout the year. The City is required to operate the dam in accordance with a dam order established by the Wisconsin Department of Natural Resources.

The DNR dam order establishes minimum and maximum levels for four different time periods throughout the year. The periods are November 1 to spring ice breakup; spring breakup to May 1: May 1 to September 15; and September 15 to October 31. The highest lake levels are allowed during the May 2 to September 15 period, to accommodate recreational activities on Rock Lake. There is also a proscribed minimum discharge from the dam, to accommodate aquatic needs of Rock Creek.

The City of Lake Mills recently adopted a new “Dam Management” Policy. The most significant change in the operation of the dam relates to lake levels. Based upon a recommendation from DNR, the City had previously operated the dam to achieve the middle of the water level ranges set forth in the DNR dam order. The order, however, does not require the dam be operated at mid-range. The City’s new policy, however, specifies that “City staff are to operate the dam to maintain target levels at the maximum” levels allowed under the DNR order. In other words, the City is operating the dam to maximize lake levels to accommodate recreational needs.

Given recent low Rock Lake levels, there is also significant interest in seeking modifications to the DNR dam order to allow additional flexibility to increase the likelihood of attaining maximum allowed levels during Summer months. There are also some glitches in the DNR order that should be clarified.

To obtain a change in the Order, however, DNR wants to know that there will not be unintended negative consequences due to any proposed change. For example, it is important to know if change in water levels would negatively impact wetlands. Consequently, DNR, the Rock Lake Improvement Association and the Jefferson County Land & Conservation Department are working together to evaluate potential wetland impacts. Importantly, the City Council also approved funding to support this effort.

Given the need to gather the necessary information, and that any change in the order will have to go through DNR’s regulatory process, any modification to the dam order will take time.

For more information regarding the Rock Lake Dam, interested citizens may go to the City of Lake Mills website Dam Management Policy - City of Lake Mills, Wisconsin (lake-mills.wi.us) or contact Eric Schreiner at 920.648.2344 or Parks@ci.lake-mills.wi.us .