This flooding is done in an attempt replicate, on a micro micro scale, how the Valley ecosystem is supposed to work. It is as much for fish as it is for birds. The shallow water is rich in nutrients that grow insects and zooplankton that allow salmon and steelhead smolts to fatten up before heading to sea.

https://watershed.ucdavis.edu/news/2...ation=node/283

You can link out from the Waterblog to a larger article on the practice.