Good question! I'm waiting to see what the answer is too!
Cecil I have a pipe that runs free water into my pond from a public reservoir 5 miles away that a recent USGS test showed detected zebra mussel DNA. We hate to cut off the free water...but we may need to...or maybe it's already too late.
http://www.tpwd.state.tx.us/newsmedia/releases/?req=20140121a