G-D Spillway water control structure
Gage Harris/USFWS.

Spillways on the refuge are simply areas where one pool flows into another. Usually it is regulated by a water control structure. Refuge staff can alter the flow of water by adding or removing boards at the structure; this alters the water level of each pool. These levels are changed throughout the year for certain management needs. Water levels are raised to provide nesting opportunities for waterfowl with limited access from predators. Higher water also gives more efficient hiding spots from fish hunting raptors. Levels can be lowered to provide mudflat habitat which species like the great blue heron use to prowl for frogs and crayfish. Although this spillway is closed to vehicle traffic, feel free to get out on foot to take a closer look.

Refuge staff altering water levels
Sara Giles/USFWS.