Watersheds

The estuary system is greatly affected by natural processes and human activities occurring in its watershed, the area of land from which water drains to tributary rivers, bayous, streams, and ultimately Galveston Bay itself. The important relationship between the bay waters and the surrounding landscape cannot be overstated: the estuary's physical, chemical, and biological quality is directly impacted by the quantity and quality of freshwater draining from its watershed.

The 24,000 square mile (62,000 square kilometer) Galveston Bay watershed dwarfs the 600 square miles covered by the bay's open waters. It reaches as far north as the Dallas-Fort Worth area, draining to the Trinity River which, in turn, ultimately flows to Galveston Bay. Due to the large areal coverage and presence of the urbanized areas within the watershed, approximately half the population of the state of Texas lives within its boundaries and has a large potential impact on the estuary.

The "lower" Galveston Bay watershed is defined as the 4,000 square mile (10,000 square kilometer) area draining to the Bay downstream of two major impoundments: Lake Houston on the San Jacinto River, and Lake Livingston on the Trinity River. Due to attenuation provided by the two reservoirs, the lower watershed more directly contributes pollutant loadings to the Galveston Bay system than does the "upper" Galveston Bay watershed. It is within this lower watershed that the Galveston Bay Estuary Program focuses its efforts.

Each stream and bayou in the lower Galveston Bay watershed has its own subwatershed. You live in a subwatershed and affect the quality of your local water body by your daily activities. In fact, contaminated storm water runoff, or non-point source pollution, from our businesses, industries, farms, roads, parking lots, septic tanks, marinas and residential yards is the number one water quality problem facing the estuary. See more about non-point source pollution in Priority Problems.

See more information on Galveston Bay watersheds in Chapter Two of The State of the Bay and in GBEP Partner Resources.