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For Cravath and Trippe Lakes opening the dams and allowing the water level slowly lower until the water level is down to a stream bead have performed a drawdown.

A Lake drawdown is one tool that can be used to manage aquatic weed problems.

Lake level drawdowns often start in the fall and continue through the winter when water recreation uses are at their lowest. Most aquatic weeds are found near the shallow shoreline.

The Cravath and Trippe Lakes drawdown started on July 8, 2019.

City Manager, Cameron Clapper and Parks & Recreation Director Eric Boettcher worked with city staff David Himself and Andy Ascher to open the dam at Cravath Lake allowing water to flow both under and over it.

Eric Boettcher, Parks and Recreation Director mentioned,

“Some other cities will drawdown during the winter seasons only and Whitewater is doing a two season drawdown for a couple reasons, being able to freeze the lakes twice so the evasive species die and on top that Whitewater is going to dredge the lake and having it last longer will dry it out more.”

Monday, July 8th was the first day to release water from the lake. A marker was painted on a nearby rock in order to monitor the amount of water dropping each day.

Cameron released more water Wednesday, July 10th. There is a drain located in the Millpond near the 5 American Flags Memorial. The water will drain here and at the bottom of the dam allowing additional water to flow under Main St. toward the creek.

This is the first step of the drawdown. Staff will monitor the amount of water that is removed from Cravath Lake and make alterations as needed to stay on track. Stay tuned for more updates as the drawdown progresses.

Why does the City want a lake drawdown you might ask?

Whitewater is trying to freeze out and control invasive aquatic plants, such as Starry Stonewort and Eurasian Milfoil. There is already a weed harvest that happens twice a season to reduce the number of weeds in the lakes.

An extended drawdown has many other benefits to the lake including sediment desiccation, which means the silty or mucky bottom can compress up to 1/3 of its depth when fully dried out. This would result in deeper water in our shallow shore areas.

This along with a dry dredging while the lake is drawn down would allow for deeper lake and a navigable channel for recreational use.

An extended drawdown also would also allow other invasive species to be controlled, while some beneficial native plants, that provide excellent fish and wildlife habitat, are expected to rebound. The extended drawdown would also give the city and/or DNR an ideal chance to inspect the dam while it’s dry.

Some worries that the community has are about what will happen to the fish in the lakes. The drawdown must happen gradually so all fish and wildlife has enough time to locate to deeper water.

“The fish are expected to move with the water as the lake level goes down. It is possible that some fish may die if they don’t move up or down stream quickly enough, but this is not expected to be significant,” said Boettcher.

After the drawdown process is complete there will be a plan in place to restock to allow for a healthier fish population to return.

Another worry from the community and the people that share the shoreline is that they are losing a couple seasons of the use of the lakes and is wondering if the drawdown will really work.

There are numerous examples in Wisconsin and elsewhere that show that Eurasian water milfoil can be substantially reduced for multiple years following an overwinter drawdown if the exposed lake bottom freezes.

Preliminary laboratory testing with starry stonewort has shown that freezing, even for short periods of time, will kill the star shaped bulbils that allow for plant regrowth.

The exposure of lake bottom sediments to dry and freezing conditions can cause the organic sediment in the exposed lakebed to compact and oxidize; increasing the water depth following the drawdown.

This oxidation can lead to increased release of phosphorus from exposed sediments initially after the lake is refilled, but less phosphorus release after the initial flush from refill. 

The extent of control of EWM and SSW and compaction of lake sediments will depend on the severity of the two winters and the amount of drawdown that is possible.

Boettcher was able to add that,

“Colder and dryer fall and winter weather will create conditions for better control of these invasive plants and organic sediments. Cracking sediment on the exposed lakebed is a sign that the lake bottom has dried enough to allow compaction of organic sediments and plant seed germination.”

The exposed sediments will be checked in winter to determine the depth of frost and freezing conditions.

The lake drawdown will continue through the spring of 2021.