Headwater spring pools and streams in the Texas Hill Country typically harbor few, if any, mussels, largely because the cool, clear waters lack sufficient phytoplankton and other foods needed to support mussel populations. There are two types of mussels that have been identified at Lyndon B. Johnson National Historical Park - the Yellow Sandshell (Lampsilis teres) and the Southern Mapleleaf (Quadrula apiculata).