The Frio River is a very clear water river. Water temp. I would say "go by the seasons". summertime water temp seems to be around upper 70's to 80's. I'm not sure on the actual length of the river(you can go on tubes or yaks).
The river has several drops consisting of 1 to 2 foot drops. Lots of bends as the river winds down through the foothills. The river offers every thing from rapids to flats to swimming holes, and fishing. The river winds through Garner St. Park, wildlife is everywhere. Every thing from birds(hawks,eagles ext..deer,turkeys,lizards.) at times the river can have many people (family groups, partiers,) floating in tubes. NO GLASS CONTAINERS ALLOWED ON RIVER!!!! CANS OR OK....
The Frio River is much like the Guadalupe river but not as cold and the water is much clearer (you can see everything in the water.) There are a lot more rapids on the Frio River.
Overall the Frio River is the best river between the three rivers (Guadalupe,Sabinal,and the frio, or the Nueces River). I haven't been there yet but they say the Nueces is dry. Overall the river is good for beginners and novice yak'ers, except when the river is high....judge yourself!
You can camp (tent) or rent cabins along the river most cabins are seasonal an range from $125.00 to 200.00 or more a night (during peak time u have to take most cabins for 3 nights) but there are many deals an cabins to stay an all of them are pretty much on the river located at many river crossings. You can find all of this info plus much more at THE TEXAS HILL REGION on the web.
From "HOUSTON" take I-10 to San Antonio then "90" to Del Rio. Go to Sabinal take right on 127. Coming from anywhere else go to "Frio River" on the web and look for "Texas hill country region", there you can get a detailed map.