The City of Yankton and the adjacent lake area have a myriad of excellent hiking and biking trails. The Auld-Brokaw Trail runs through the entire city and actually connects to the trail out to Lewis and Clark Lake. From there the trails continue to run through the state recreation area. There are number of primitive hiking trails at Lewis and Clark Recreation Area, as well as a horse trail.
And, don't forget to take a walk across the Meridian Bridge in downtown Yankton. This double decker bridge is now a pedestrian walking trail connecting Yankton to Nebraska across the beautiful Missouri River.
With the lake and the trails, Yankton hosts a triathlon and some significant road races throughout the year.