I am pretty sure what I have is water primrose. Later in the season it forms mats on the water and has a small yellow blooms. It is just now starting to come up again this year.

Last year I had to get in the water and pull it out by hand. It has lots of roots hanging down under the mat and not all of the roots are attached to the bottom.

How do I kill it with out hanging to get in the water and pull it out?

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.

Using a systematic herbicide with a surfactant will control water primrose. Treating it early is best and not waiting. Gylphosate applied properly will give good results on water primrose.

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.