Some kind of herbicide. Call your county's Extension office for recommendations and instructions. The extension agent there might not know, but they'll connect you with a specialist in the A&M system who does. I'm not familiar with Texas rules on aquatic herbicides so I don't want to throw something out there that you couldn't use.
Right now is a great time to treat. Much easier to control any weed if you hit it early.
Just seen this. Last year it almost took over 1/4 of my 2 acre tank. This year spayed Gylphosate i bought at tractor supply on a small portion and it worked. Gonna treat it in stages so the plant kill won't starve the oxygen out of the water and cause a fish kill.