For a pictoral record of the trip that Steve and I took, with commentary, go to the following url: http://users.ev1.net/~spituch/a.html
Scroll down to the "Expedition I" link, and click on that. Before looking at all the pictures, click on the map link to the left on the first page.
We found the following species at the put-in:
Hydrilla verticillata, Hygrophila polysperma, Potamogeton sp?, Ceratopteris thalictroides, Ceratophyllum demersum, Hydrocotyle verticillata, Sagittaria sp. (platyphylla?), Ludwigia repens or palustris?, Pista stratiodes, Eichornia crassipes.
After the second railroad crossing, we found a Cambomba sp (caroliniana?). Below the first dam a water cress, Nuphar lutea, and Riccia showed up. Below the third dam (lunch stop), we found Zosterella dubia. Finally, the C. beckettii? showed up just past the point where the sewage treatment plant emptied the treated water into the river. We were careful not to dislodge any crypts when we gathered our sample. In the summer, the river fills up with tubers (people floating down on inner tubes), and they no doubt loosen some crypts and contribute to the spread of the species. Large patches of crypts continued to be seen until the river became too deep due to the back-up from the Cummings dam to see the bottom. On the faces of some of the dams we found Samolus valerandi and what might be Lobelia cardinalis.
So, don't say you can't find aquatic plants in Texas!