Harmful invasive species found at Medina Lake; Lake Placid now ‘fully infested’ with zebra mussels Zebra mussels could spread downstream, TPWD officials warn Tags: SAN ANTONIO – Invasive zebra mussels that are known to harm wildlife have been detected at Medina Lake and could spread to nearby waterways, according to the Texas Parks and Wildlife Department. TPWD on Tuesday announced that the detection marks the first time zebra mussels have been found in the San Antonio River Basin. They were detected on Feb. 11 when someone showed TPWD officials an image of a zebra mussel at a boat ramp near Haby’s Cove. Biologists soon after discovered two zebra mussels attached to rocks in the area near Red Cove Marina.