Galveston Bay is the most prominent geologic feature on the upper Texas coast. It is the state’s largest bay, covering about 600 square miles, situated in one of its most urbanized and industrialized areas. Beyond this, the Galveston Bay watershed—or the area of land that drains into a given waterbody—is about 24,000 square miles, stretching from the Houston metropolitan area north along the Trinity River basin past the Dallas-Fort Worth metroplex. Half the population of Texas currently lives in the Galveston Bay watershed.
Galveston Bay is, by definition, an estuary—a semi-enclosed coastal body of water which has a free connection with the open sea and within which sea water mixes with fresh water from the land. In the case of Galveston Bay, it is where fresh water from the Trinity and San Jacinto Rivers and the extensive bayous and creeks of the “Bayou City” and surrounding areas mix with the salty water of the Gulf of Mexico. With an average depth of about eight feet, the bay contains approximately three million acre-feet of water. Inflows of fresh water from rivers, bayous, and streams are the lifeblood of an estuary, bringing in nutrients that fuel the food chain and sediments to replenish our wetlands. Because of this, estuaries are among the most productive ecosystems in the world. They are home to a huge amount of plant and animal life and can produce large harvests of recreational and commercial fish and shellfish. Ninety-five percent of commercially and recreationally important fisheries species in the Gulf of Mexico are dependent upon estuaries like Galveston Bay during some part of their life cycle. Galveston Bay is the most productive bay in Texas and one of the most productive bays in the country, trailing only Chesapeake Bay, which is eight times its size.