During July 2000–September 2002, the U.S. Geological Survey collected and analyzed site-specific hydrologic, water-quality, and biological data in Dickinson Bayou, Armand Bayou, and the San Bernard River in the Gulf Coastal Plain of Texas. Segments of the three water bodies are on the State 303(d) list. Continuous monitoring showed that seasonal variations in water temperature, specific conductance, pH, and dissolved oxygen in all three water bodies were similar to those observed at U.S. Geological Survey stations along the Texas Gulf Coast. In particular, water temperature and dissolved oxygen are inversely related. Periods of smallest dissolved oxygen concentrations generally occurred in the summer months when water temperatures were highest. Water-quality monitors were deployed at three depths in Dickinson Bayou. For periodically collected nutrients, the median concentration of ammonia nitrogen was largest in Dickinson Bayou and smallest in the San Bernard River. Median concentrations of ammonia plus organic nitrogen, nitrite plus nitrate nitrogen, and orthophosphorus were largest in Armand Bayou. The median concentration of each of the four nutrients was larger for high-flow samples than for low-flow samples. The largest individual nutrient concentrations occurred during spring and summer. Both median and individual concentrations of chlorophyll-a were largest for Armand Bayou; median concentrations of pheophyton were similar for all three water bodies, and individual concentrations were largest for Armand Bayou. Median densities of fecal coliform bacteria and E. coli bacteria were similar for all three water bodies. Flow conditions had minimal effect on concentrations of chlorophyll-a and pheophytin, but the largest bacteria densities were in samples collected during high flow. Yields of most nutrients tended to increase with distance downstream. Yields in the San Bernard River and tributaries were less than yields in Dickinson and Armand Bayous. For Dickinson and Armand Bayous, the most individuals and species of fish were collected at the most downstream main stem site; for the San Bernard River, the fewest individuals and species of fish were collected at the most downstream main stem site.