The Laguna Madre is a large body of shallow water separating Padre Island from the South Texas mainland. It covers 609 square miles of estuarine and coastal marine systems. Since no major rivers flow into the Laguna Madre, its salt content is quite high, about 35 parts per 1000 parts of water. This increases to 45 parts per 1000 parts of water in the Lower Laguna Madre and during periods of hot, dry weather.
The average water depth is about 2. 5 feet, with some areas reaching a depth of 5 feet. Variable depths and salinity support different types of seagrasses, hyper-saline marshes, algal flats, and lomas. The Laguna Madre is an important breeding ground for many aquatic birds, as well as an important wintering and stopover area for numerous species. The extremely shallow areas provide excellent feeding grounds for winter duck populations which number in the thousands. Seagrasses are the main winter food source for Redhead ducks. The Laguna Madre is the summer nursery area for young brown shrimp. Skipjacks, pinfish, broad killifish and striped mullet forage in the shoalgrass areas. Mollusks and crustaceans, generally associated with the areas of underwater vegetation, are important as waterfowl food.