Lake Erie water levels change on short-term (daily and seasonally) and on long-term scales (over days, months, years, and decades). The longer-term levels are determined by changes in the net supply of water received from the watershed and the upper Great Lakes on a seasonal and annual basis. Storm surges and seiche events (long waves that will move back and forth as they reflect off the opposite ends of the basin) cause changes on a daily or weekly basis (Lee et al. 1996). Historically, the natural water level of the lake has varied over a range of about 2 meters (6 feet) (Lenters 2001; Quinn 2002; Lofgren et al. 2002) and the lake level has tended to cycle through highs and lows over 30-year periods. High-water periods were recorded in Lake Erie in the 1950s and 1980s-1990s, while low-water periods have occurred in the 1930s and 1960s.

Changing water levels and the resulting shifts in the location of the shoreline and the littoral zone have an important impact on structure, function and productivity in aquatic systems (Chubb and Liston 1985). Given the relatively flat topography associated with Lake Erie, Lake St. Clair, and associated connecting channels, large expanses of shoreline areas typically become inundated and/or exposed when the lake level changes. Changes in surface water, water exchange, and the ability of fish to move between coastal wetlands, embankments, and the open lake are directly related to the size, timing, duration, frequency, and rate of change of these fluctuating water levels (S.D. Mackey, pers. Comm)