Freshwater mussels (Family Unionidae) have gained increasing recognition as important elements of aquatic ecosystems, indicators of environmental degradation, and economically significant objects of commercial and sport fisheries. However, they have also been recognized as the most rapidly-declining faunal group in North America. Texas Parks and Wildlife Department began to address these issues in January 1992 when Heart of the Hills Research Station (HOH) initiated statewide unionid surveys and research into mussel biology. These efforts have subsequently revealed relationships between flow rates and water levels associated with mussel survival and losses. Initial results indicated numerous waters in Texas where mussel populations had been reduced or eliminated due to changes in flow rates and water levels. River bed scouring was found to be one of the most widely ranging factors in mussel declines. Overgrazing, land clearing, highway construction, impervious surfaces associated with general human development, increased rainfall, increasing frequency of severe storms, and patterns of reservoir water releases have contributed to scouring problems. Many of these same factors have also resulted in excess deposition of sand and silt in other areas resulting in smothered mussel beds and unacceptable habitat changes. Some manipulation of reservoir water levels has also been found to be detrimental to mussel survival. Rapid, dramatic, and long-duration changes in water level have been observed to be far more destructive than slow, limited changes for shorter time periods. Some such factors are necessarily linked to human activity, but others are unnecessary or could be easily modified or eliminated.