The bayou is an open system that receives substantial inputs of fresh water, sediment, and nutrients from surrounding upland areas and tributaries. Subsidence in the watershed has virtually eliminated the coastal marshes, extended the zone of tidal influence, and changed the lower reach of the bayou from a fresh to a brackish water environment. The Christmas Bay Coastal Preserve is located in the southwestern portion of the Galveston Bay system in Brazoria County. The preserve is home to migratory and resident waterfowl and shorebirds. Christmas Bay, a small secondary bay at the southwestern extreme of the Galveston Bay system, is an important finfish and shellfish nursery area.
Seagrasses are probably the most valuable and productive habitats in the bay.
Brazoria National Wildlife Refuge is adjacent to Christmas Bay and has been a major, positive influence on the health and maintenance of the Christmas Bay ecosystem. Welder Flats is located in the San Antonio Bay System in Calhoun County. This preserve contains submerged coastal wetlands and numerous species of wading and shore birds, including the whooping crane. Welder Flats is located on the eastern shore of middle San Antonio Bay. The characteristic mid-bay wetlands of Welder Flats consist of saltwater marshes, submerged aquatic vegetation, unvegetated sand and mud flats, and shallow saltwater ponds and lagoons.