your bud Richard W would be the guy to ask about that
... but, for what it's worth, here's an article about the "return" of aquatic veggies to Ky Lake ---
http://www.parislanding.com/aquatic_vegetation_2.htm
As for the Zebra's ... yes, they are there and well established. And since 1 sq meter can hold as many as 70,000 of them ... and they can run a litre of water thru their systems in 24hrs -- then, yes, I'd say they have had a big impact on the water clarity. They're plankton filterers ... so they do compete with fry and other plankton eaters (like Shad). And, the high rate of filtration they are capable of, means the water should get clearer - even if only from the fact of the removal of the plankton. KY & Barkley lakes are what they are, with regard to being such prolific producers of fish, simply because they don't hold their water very long. The constant influx of "new" water, bringing all the nutrients & such, is crucial to sustaining the vegetation growth - as well as the growth of the young fish & baitfish. I think the Zebra's have had some effect on the return of vegetation to these lakes -- but, maybe not nearly so much as the TVA decision to not eradicate the weeds. If the Zebra's didn't do the damage, that they are capable of, they might even be considered a "help". But, displacing the native mussels, clogging drains (on boats and dams), filtering out the foodsource that's vital to fry and baitfish, and the end result of collecting high concentrations of PCB's and passing them on to any fish/animal that consumes them ......... keeps them in the "invasive pest" catagory - and being virtually impossible to eradicate, makes them a problem that there doesn't seem to be a solution to. .................cp