U.S. Army Corps of Engineers river stage and discharge data (www.rivergages.com) were used to calculate longitudinal connectivity, which is represented by the number of days each lock and dam is in “open river” conditions. During high water conditions, dam gates are generally lifted out of the water or lowered to the river bottom, removing physical barriers to passage (“open river condition”). Each lock and dam in the Upper Impounded and Lower Impounded Reaches has a specific discharge or stage that when reached, results in open river conditions. For each lock and dam, we calculated the average annual number of days in which daily discharge or stage would have resulted in open river conditions between 1985 and 2015. The lock and dams on the Illinois River Reach do not have specific capacities, but records of when the dams are opened and closed were used to estimate criteria for open-river conditions (T. Knox, U.S Army Corps of Engineers, personal communication, 2017) and calculate the percent time in which the dam was in open river conditions over the same period.