The slight difference between the two lakes is associated with the degree of nonpoint-source pollution, possibly from shoreline urbanization. The shoreline of Lake Marble Falls is approximately 40 to 50 percent developed, compared to less than 10 percent for Lake Travis. Lake Marble Falls is more susceptible to immediate shoreline development since the water level of the lake typically does not vary significantly. Since Lake Travis is a flood control lake, the level fluctuates depending on weather conditions. So development at the water's edge is not feasible.
Development can increase the amount of runoff, contributing to nonpoint-source pollution.
Water in Lake Marble Falls has a much shorter retention time than Lake Travis. Since the velocity of water in Lake Marble Falls is much faster, some water quality tests tend to show higher concentrations of pollutants because there is less time for pollutants to settle out. Major concerns in and around the two lakes include the effects of the drought and the frequency of algae blooms. The effects of the 1996 drought on water quantity and quality were felt throughout the basin. Many creeks quit flowing and either became intermittent with pools or dried up.