Probably has more to do with the info below than anything else... hard to argue with 30 years of scientific research when battling to keep an invasive species in our lakes.
"This plant forms dense mats at the surface of the water. It changes pH, removes oxygen, restricts native plant growth, block out nutrients for aquatic animals, hinders irrigation, recreation and water flow. It is extremely competitive and resilient, surviving freezing or drought because it can break off into portions and sink down to safer waters. It is easily spread through boating and fishing activities and by waterfowl.
In North Carolina and Florida, hydrilla is a suitable habitat to grow a deadly algae Aetokthonos hydrillicola. This algae produces a neuro-toxin, that has been linked to the death of several bald eagles and coots. So little is known about this new algae, researchers aren't sure what the chemical makeup of the neuro-toxin is. However, it has been found on Eurasian milfoil and Brazilian elodea; emphasizing the necessity to remove these invasive aquatic plants."
"Hydrilla is one of the most invasive weeds in the world, and it is capable of clogging waterways, and even public water supplies. It is now illegal to possess or transport this species in Texas, and is also listed as a
Federal Noxious Weeds.
Despite 30 years of research and intensive management efforts, hydrilla is still a major problem where it is successfully established."http://www.tsusinvasives.org/home/database/hydrilla-verticillata