Hmmmm... I guess it depends on what you're looking for.
IMHO, Spring Lake at Aquarena Center in San Marcos is the best freshwater diving in Texas. The water is clear and a constant ~72° top to bottom all year. There's even a warming hut for changing when it's cold out (air conditioned when it's hot out.) The lake is full of life including lots of different kinds of fish, turtles, snails, diving ducks and cormorants, and even the occasional nutria. The bubbling springs are fun to watch and the plantlife is prolific and varied. (OK it's mostly hydrilla, but lots of other plants are there too if you look.) The downside is you have to take the Scientific Diver Authorization to Dive course before you can dive there, and you have to be working on a project while you're there. It's not the place to go if you like to go deep either- I think 27' is the deepest I've gone. The diving here is equal to the spring diving I've done in Florida (but without the caves or manatees, of course.) (
http://www.continuing-ed.swt.edu/aquarena/home.html)
My second choice is Clear Springs Scuba Park in Terrell (CSSP). In the summer it is a lot like Spring Lake with clear water and abundant life, but the water isn't quite as clear nor the life quite as abundant or varied. The lake is "spring fed", but unlike the millions of gallons of flow from the springs at Spring Lake, the CSSP springs only flow enough to counter evaporation- there's no outflow spring run from the lake. With no outflow, the temp varies with depth and season, and in winter the whole lake gets cold and the life pretty much disappears. Max depth is just under 60'. Due to its location near home, it's becoming my most frequent dive site. (
http://www.geocities.com/clearspringsscubapark/)
Balmorhea State Park is a neat freshwater dive with lots of fish and turtles. It's pretty far from here and the lake/swimming pool is fairly small and shallow (maybe 30-40'?) but it's clear and warm in the winter. I dived it once ~12 years ago and have fond memories. When I dived there they only allowed divers in the winter when there were no swimmers. Dunno if that's still the case. (
http://www.tpwd.state.tx.us/park/balmorhe/)
Possum Kingdom Lake and Lake Travis are pretty equivalent in my book. Both have very variable temps and vis depending on the season. Both have some life, but not to rival the above locations. The wall diving is kinda cool and you can get deep in either lake if you want to.
Athens Scuba Park and Blue Lagoon are also pretty equivalent to me. Both have reasonably clear water, but I suspect they are so clear because they are so toxic. (Dunno if it's just the pH, added chemicals, or what.) There's hardly any life at all in either. Athens Scuba Park has a
lot of sunken junk to dive around and through if you like that kind of thing. I rinse my gear
very thoroughly after diving in either. I don't think I got below 25' in either. (
http://www.athensscubapark.com/home.htm)
I haven't tried any other freshwater dives because none have seemed to offer anything different from the locales I mentioned above. I'm game to try new places if there's a group going though.
Just my 2¢,
Bill