Aquatic Invasive Species Snapshot Day, 2025

by Sheila Leary

We had more than 40 enthusiastic volunteers this year to survey 24 Dane County sites for aquatic invasive species. After a brief training session at Warner Park, teams fanned out to sample the waters in the upper Yahara River, Lake Mendota, Six Mile Creek, Dorn Creek, Token Creek, Castle Creek, Warner Park Lagoon, Tenney Park Lagoon, Yahara River at Tenney Park, Lake Wingra, and Wingra Creek.

Friends of Cherokee Marsh acts as the Dane County local host for Snapshot Day, recruiting volunteers and publicizing the event. We are aided each year by a scientific expert from UW Extension, the DNR, or Dane County. Snapshot Day is a statewide annual effort of the UW-Extension Aquatic Invasive Species Program and the Wisconsin Department of Natural Resources.

Volunteers located Eurasian watermilfoil, zebra mussels, curly-leaf pondweed, New Zealand mudsnails, Japanese knotweed, and Chinese mystery snails at the various sites. The (sort of) good news is that none of these populations are new finds.

Specifically in the Upper Yahara or in Cherokee "Lake," volunteers found Chinese Mystery Snail, Curly-Leaf Pondweed, and Eurasian Water-Milfoil, which had all been found there before.

Chinese mystery snails might be attributed to people dumping exotic aquarium species into streams and wetlands. The CMS is an invasive freshwater aquatic snail native to Southeast Asia and Eastern Russia. Once they have become established in an ecosystem, this invader outcompetes native mollusks and filter feeders for food and habitat, and their high filtration rate displayed when feeding can lead to water quality issues comparable to that of invasive zebra and quagga mussels. By closing the opening of their shell with their operculum, adult Chinese Mystery Snails can survive out of water for at least 4 weeks!

Curly-leaf pondweed is native to Eurasia, Africa, and Australia. It was likely introduced when common carp were intentionally introduced into Midwest waters as a game fish in the 1880s. The species was likely spread through the movement of watercraft and water-related equipment. Curly-leaf pondweed can form dense mats at the water’s surface that inhibit water recreationists; overtakes habitat and outcompetes native aquatic plants; and midsummer die-offs can litter the shoreline with dead plants.

Eurasian water-milfoil is native to Europe and Asia. It was discovered in the eastern United States in the early 1900s. The species was likely introduced and spread through the movement of watercraft and water-related equipment. It causes problems similar to curly-leaf pondweed.