SYMPOSIUM PRESENTER CO-AUTHORS: David Marshall (Underwater Habitat Investigations, LLC) TITLE: The future of the fishes of the Lower Wisconsin River floodplain ABSTRACT: The Lower Wisconsin River (LWR) is one of the highest-quality large-river ecosystems remaining in the Midwest. It has a largely intact floodplain with extensive riverine wetlands (backwaters, sloughs, floodplain lakes and ponds, marshes, and seasonally flooded forests) that support a diverse fish community of more than 30 species, distinct from the diverse fish community found in the flowing water of the river channel. Several of the floodplain species are otherwise uncommon in Wisconsin, most notably the state endangered starhead topminnow (Fundulus dispar). However, the wetland fish community is threatened by intensive agriculture in the sandy terraces adjacent to the floodplain. Excessive nitrate that leaches from these heavily fertilized crop fields readily enters the shallow groundwater and rapidly moves into the wetlands. This has led to huge summer blooms of filamentous algae and duckweed that have shaded out essential native macrophytes and degraded water quality to the point that many localized fish populations have declined sharply or been eliminated. Alarmingly, no effective regulatory mechanism is available to curtail this ongoing biodiversity loss. On the positive side, an ongoing effort has successfully established new populations of the starhead topminnow and another uncommon species, the lake chubsucker (Erimyzon sucetta), from the LWR floodplain into non-agricultural floodplain habitats upstream of the Prairie du Sac Dam. Looking forward, the possible effects of climate change on LWR floodplain fishes, particularly milder temperatures and increased flooding, are highly uncertain but could be positive, if more water on the floodplain means more wetland habitat and better water quality. BIO: John Lyons is the Curator of Fishes of the UW Zoological Museum in Madison, a position he has held since retiring in 2017 after nearly 33 years as a fisheries research scientist and supervisor for the Wisconsin DNR. He has studied the fishes of the Lower Wisconsin River for more than 40 years. He holds a PhD from UW-Madison with an emphasis on fish ecology.