The 2021 winter lake level target range for Winnebago is between 1.2 and 1.4 feet. The winter drawdown target is decided by the Army Corps after a public conference call that is held each winter. They make their decision based on public input and conditions in the watershed (snowpack, depth to frost, precipitation forecast, and weather outlook).

The Army Corps successfully met the 2021 winter drawdown target and held the lake within the winter drawdown range for most of March. This follows their annual strategy for regulating the outflows of Lake Winnebago. According to historical records, Lake Winnebago for the first weeks of March was within one inch of a 70-year average.

This purpose of winter drawdown is to create room for Lake Winnebago to store water from spring snow melt and precipitation. This helps to prevent flooding when spring inflows to Lake Winnebago from over 5,900 square miles of land exceed outflow capacity of the dams. This leads to uncontrolled rise in lake level in the spring and if Lake Winnebago is not low enough when this occurs, flooding along with damage to habitat and shorelines ensues.

Despite winter drawdown on Lake Winnebago being an annual occurrence for the past several decades, this year seemed to draw an unprecedented amount of attention from lake users, shoreline property owners and the local media.

The typical winter drawdown may seem new to some because people usually wait until April or May to think about boating. However, the desire for many people to get back outside after a long COVID-19 winter combined with warmer than usual March temperatures has more people looking to the lake much earlier this year than usual. Without snow cover from a mid to late March snow storm and ice conditions having deteriorated early on this winter, the mud flats are highly visible in contrast to the water’s edge. An added factor is that in recent memory (the last handful of years) the lakes have had too much water because of record breaking precipitation and saturated conditions that persisted for multiple years in a row.

Inflows to the lake have been gradually increasing over the past week which resulted in Lake Winnebago’s water level exceeding the 1.4 ft. winter target range. As of the morning of March 26th, 2021, the lake was at 1.61 ft. Ice off (when there is no ice left on the lake) marks the official start of lake refill which usually occurs around April 1st each year.

The extra attention being paid to winter drawdown levels is likely the result of several factors including:

  • The Army Corps successfully meeting the winter drawdown target and holding the lake within the winter drawdown range (1.2 to 1.4 ft) for more than two weeks.
  • Warmer than usual March temperatures
  • Lack of snow cover on and around the lake leaving mud flats exposed
  • Poor ice conditions on the lake in early March

The image below shows the water level strategy versus actual average water level measured in Lake Winnebago over the past three years. The dashed  line represents the measurement for that year while the dotted line represents the average across a set of years.

Year to Date Actual Trend versus Annual Strategy (September 2018 to March 2021)

At the beginning of April, the Army Corps will gradually refill the lake with a spring target of approximately 2.5 ft. by May 1st and 2.9 ft. by June 15th for the navigation season. The Army Corps will then attempt to hold the lake between 2.8 ft. and 3.0 ft. through October 1st. This follows an annual strategy set by the Army Corps with stakeholder input.

While some people have expressed concern or frustration about the low winter water level, others have praised the Army Corps for their efforts in preventing ice shove damage and shoreline erosion. The extra attention to water levels is an excellent opportunity for people to learn more about management in the Winnebago Lakes. Information about the historical impacts of water level fluctuations and an overview of current water level management has been documented in a report published last year. CLICK HERE to view that report.

An opportunity to be part of the conversation

For those who may be interested in being an active voice in discussions related to water levels in Lake Winnebago, we invite you to consider joining the Winnebago Water Level Assessment Team (WWLAT). The purpose of the WWLAT is to provide opportunities for lake users, other stakeholders, and experts to collaboratively develop realistic and achievable water level strategy recommendations that reasonably balance the top priorities of multiple system users and the health of the lakes. If you are interested, please contact Korin Doering at korin@fwwa.org or (920) 851-0948.

More information about water level management is also available on the Army Corps website, including periodic updates of current conditions: https://www.lrc.usace.army.mil/…/Water…/Lake-Winnebago/

NOTICE: The Army Corps will be hosting a conference call on Tuesday, April 6th, 2021 at 6:00 pm. The call is open to the public and the focus will be on the regulation of water levels on Lake Winnebago and impacts to other areas of the watershed. CLICK HERE for more info.