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.
Pools in intermittent creeks were prone to algae blooms and fish kills as dissolved oxygen levels dropped. Also, there were more complaints about algae blooms in 1996 on Lake Travis than in the previous two years. Nonpoint-source pollution is carried into lakes and streams during rains that wash pollutants off the surrounding land. Lake Austin has only two major tributaries, Bull Creek and Bee Creek, while Town Lake has nine tributaries. Most of the water flowing through Lake Austin is from water released from the bottom of Lake Travis.