Fieldwork on a Flooded Fish Lake

by Anna Mueller – Located just east of Sauk City, about 30 min northwest of Madison, Fish Lake is a bizarre and interesting place. Although it has experienced flooding since the ‘80s, in the past 15 years it has become permanently flooded. In the 2000s, houses were evacuated, and the entire road is now underwater, leaving an eerie underwater pathway, lined with the rooftops of flooded homes and RVs. I recently joined Cassie Ceballos’ team for their weekly field work at Fish Lake, where a ring of dead trees surrounds the shore and the water literally creeps towards the houses that remain on its banks. 

Fish Lake is a seepage lake, meaning that rising groundwater seeps into the bottom of the lake, potentially causing water levels to rise. In addition, it has no outlet. The flooding has created a unique ecosystem where the littoral zone (the area where the water meets the shore) was previously terrestrial, but is now aquatic. Cassie and her undergraduate assistants, Lila and Zach, visit the lake once a week, taking water samples, and observing and collecting aquatic plants. They want to know how the flooding has changed the water chemistry, zooplankton and plant communities, and sediment. 

Cassie and her team head to a sample site on Fish Lake. Dead trees in the background mark just how high water levels have risen. Photo: Anna Mueller

The team visits six sites, five of which follow the shoreline, and one located at the deepest point of the lake. At each site, they spend ten to fifteen minutes collecting data. The depth of the water is measured, usually between 1.5- 2 meters along the shore. In addition, a Pro DSS instrument is used for a plethora of measurements including Ph, conductivity, pressure, temperature, dissolved oxygen, and chlorophyll, which is cross checked with chlorophyll that they collect with filters back at the lab. They sample the water for suspended solids, nitrogen, and phosphorus as well. A zooplankton net is used to collect samples of the zooplankton living along the shore, often around dead trees and forest debris. 

A hand holds a vial filled with green liquid - a plankton sample researchers took from a lake.
Close up of a plankton sample the team took during their sampling. Photo: Anna Mueller

One of the sites is located over the flooded road. Water smartweed, distinguished by its small, fuzzy pink flowers, lines the sides of where the road used to exist, as well as other sections of the lake that were previously terrestrial. A hardy native plant, smartweed can be both terrestrial and aquatic and Cassie’s team has noticed that it appears to host many other organisms. They are currently studying the role of smartweed in Fish Lake’s littoral zone. 

While along the shore, we identifies local birds, spotted a bald eagle, and kept a lookout for interesting plants or new organisms. Any interesting find was transferred to a bag or container to be studied later in the lab. This is science at its best; observing and discovering new things spontaneously, while still systematically maintaining a consistent record of data.



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