As part of the Mississippi Flyway, the Odessa complex contributes scarce, high quality migration habitat in a landscape dominated by agricultural production. The Mississippi Flyway is a globally significant flyway for 60% of all North American bird species and provides a major route used by shorebirds, ducks, geese, blackbirds, warblers, sparrows, and thrushes. It contains the longest migration route of any route spanning the Western Hemisphere, more than 3000 miles from the mouth of the Mackenzie River to the delta of the Mississippi River. This flyway supports an average of 36 percent of all ducks in the contiguous United States and most of the mallards in North America use the flyway. Most North American land birds that winter in the tropics also use this flyway.
The Odessa complex represents a small fragment of the vast expanse of shallow wetlands that covered the Mississippi River floodplain when European settlers began arriving in the early 1800s. In those days, spring floods spread out over the entire floodplain and filled thousands of shallow basins and sloughs scattered from bluff to bluff. Many of those basins would dry during late spring and summer, and a variety of wetland plants would germinate and grow in them. Depending on depth and soils, some would be dominated by perennial plants like cattails, bulrush or buttonbush, and others would grow annual seed-producing plants like smartweeds and millets. Normal fall rains produced a slight rise in the river that filled many of those basins again, making all that seed available to migrating waterfowl. In the spring, those heavily vegetated basins produce an eruption of tiny aquatic organisms, including insect larvae, tiny crustaceans, and others that biologists refer to generally as invertebrates. They supply spring migrating waterfowl a crucial source of protein for their northward journey, especially to hens building energy reserves for egg laying. Ideal conditions wouldn't have been present everywhere on the river every year, but because of the vast resources stretching its length from bluff to bluff, vast areas would have been present for birds to refuel on their migration.
Today, the river and floodplain are now a completely different system. The river has been reduced to a narrow ribbon cut off from most of the floodplain by adjacent levees, and drainage systems keep most of the floodplain dry year around for agriculture and other development. The river itself has been converted to a series of impoundments by the navigation dams, and while it still floods, the drying cycle has been eliminated and so too has most of the wetland vegetation that once sheltered and fed migrating waterfowl.
At the Odessa Complex, managers have a unique opportunity to mimic the historic water level fluctuations that produce everything the waterfowl and other migratory birds need during their migrations. An inlet structure above Lock and Dam 17 allows water to flow in from the pool, while an outlet structure below the dam allows water to be drained into the lower pool 18. The normal operation is to slowly drain water out of the Complex once the spring flooding is over to reach the lowest levels by mid-summer when nearly a thousand acres of mudflats are exposed. Those mudflats will sprout a profusion of seed-producing moist soil plants if water is kept off them for a month or so. When the water is slowly raised throughout the fall to incrementally flood each slight rise in elevation, the birds can take advantage of the different food that has been produced at each of those levels. A maximum fall level is usually reached by late November. However, water level management at Odessa is not always that simple… Flooding on the Mississippi or Iowa Rivers along with heavy localized rain events may impact the water level drastically at any time.
The current Odessa water level gage reading at Schafer’s Access can be found here: http://water.weather.gov/ahps2/hydrograph.php?wfo=dvn&gage=odsi4