Before European settlement, wetlands covered roughly 11 percent of Iowa. The slow-moving waters provided habitat for a variety of species, including the diminutive Topeka shiner—a three-inch silvery minnow with bright orange fins that pop against its pink body during breeding season.
Then came industrial agriculture. Tile drainage systems transformed Iowa's landscape, draining over 95 percent of those wetlands into cropland. Rivers that once meandered lazily began flowing faster and fuller. The U-shaped oxbow ponds that formed when rivers changed course—natural refuges where small fish could reproduce away from predators—filled with agricultural sediment.
By the turn of the 21st century, Topeka shiner populations had collapsed to just 20 percent of their original geographic range across Minnesota, South Dakota, Iowa, Nebraska, Missouri, and Kansas. In 1998, the species landed on the federal Endangered Species List.
That's when the restoration work began. In 2000, the US Fish and Wildlife Service partnered with the Nature Conservancy's Iowa chapter to identify and excavate former oxbow sites, digging through decades of soil erosion to reach the old creek beds. When they hit those original depths, groundwater would bubble up, keeping the ponds from freezing solid in winter—exactly what the hardy shiners needed to survive.
The fish returned. Topeka shiners now appear in 60 percent of the more than 200 restored oxbows across Iowa's predominantly private farmland. A 2021 status review recommended moving the species from "endangered" to "threatened"—a significant conservation victory.
But conservationists discovered something equally valuable. Agricultural pollutants in nearby waterways were settling in the oxbow mud, effectively washing out the streams. "It really is a success story," said Karen Wilke, associate director of freshwater at the Nature Conservancy in Iowa. "Now we're not just doing it for Topeka shiner, but we're doing it for water quality as well."
The oxbows reduce nitrate by around 50 percent, providing benefits far beyond one species. Researchers have found up to 30 distinct fish species in a single half-acre oxbow. Since 2019 alone, the Iowa Topeka Shiner Recovery Partnership has completed over 70 restoration projects with 40 more underway—and farmers are increasingly eager to participate in protecting these unexpected allies in both conservation and water quality.