The combination of sunlight and saline waters yields a rich crop of marsh grass that dies in the fall, is harvested by winter high tides and is distributed as nutrient debris to the estuarine food web. Across the broad tide flats , eelgrass meadows provide sheltered habitat and act as a nursery for a variety of fish, crabs, and other creatures. Its rhizomes are buried in the mud and so stabilize sediments and prevent erosion. Eelgrass grows rapidly in sunlight, fixes nutrients from mud and water, and generates detritus which releases nutrients to the food web as it decays. Eelgrass growth is adversely affected by turbidity.
Flats are the result of thousands of years of sedimentary deposit onto the bottom of the estuary.
As rivers and streams reach seal level, they lose energy necessary to retain their load of sand, clay and organic debris. Logging and road building in the watershed during modern times hastened erosion, added to the sediment load, and contributed to rapid filling of estuaries over the last century. Continuously submerged, the deep channels of the estuary are conduits for many species of marine life to enter and leave the bay. Jellyfish float near the surface while marine fish move with the more saline waters of the bottom. In these channels, salmon and shad migrate downstream through the estuary to the ocean.