5of5 Zebra mussels are spreading like wildfire yet again, and this year, they're closer to San Antonio than ever. Lake Placid, which is 36 miles outside of San Antonio, was designated by Texas Parks and Wildlife Department as “fully infested" on Tuesday, while Lake Medina was named "positive" for the pests. The discovery of the invasive species at Medina marks the first time the critters have been found in the San Antonio river basin, according to TPWD. The mollusk spreads when aquatic equipment, like boats, are not cleaned and dried properly before being moved and used on uninfected waters. The department said in a press release that they investigated the Medina infestation after a lake visitor sent a photo of the striped creatures near a boat ramp by Haby's Cove.