Tim, the latest (last three years) of TPWD magazine pics of Caddo show no water visible at all, only a field of green with a canoe/kayak in it. I forget the name of the stuff but it a very tiny floating leaf thing, maybe 3mm wide. I'm aware of the campaign to keep things like salvia and zebra mussels from hitchhiking. Most park boat ramps have no wash facilities, so I'm not sure what can be done.