This study was designed to characterize the quality of Houston area stormwater and its potential impact on receiving waters, including Galveston Bay. Stormwater samples were analyzed with regard to standard water quality parameters, as well as for metals. Large increases in the concentration of particles, suspended solids, organic carbon, iron, mercury and zinc were observed in storm runoff. Concentrations of barium and strontium, which occur naturally in area soils, decreased as result of a storm. Data suggested a link between increasing concentrations of smaller solids (0.45-20μm) and that of iron and mercury. Organic carbon showed evidence of being similarly related to zinc and larger solids ($>20\mu$m). Higher concentrations of these materials, in conjunction with increased runoff flows, resulted in storm loadings equivalent to months or even years of background flow. Particle size distributions measured in situ and laboratory simulations indicated significant aggregation in the runoff stream.