Lady Bird Lake
You can rent a canoe, kayak, or paddleboard at numerous locations. Zilker park below the pool on the south side, http://www.texasrowingcenter.com and http://www.rowingdock.com/ on the north side. There is a free ramp and decent parking under I-35 and right across the street from the sports fields next to Austin High. You can also launch under the Mopac with a small kayak.
Mansfield Dam Park
20 minutes form downtown Austin, this hidden gem features good bass fishing, easy launch, and great views. There is also a small bridge that your not supposed to jump off of. It’s the start of lake Austin.
The downstream side of the Lake closest to Austin is too big with too many big boat for a kayak or paddle board. If you venture up upstream on either side of the lake the waters shallow, the big boats disrepair and paddling starts to get nice.
The Guadalupe River
For those looking for a adventure, the Guadalupe river is an action packed destination. In the summer the river is filled with tubers. The flow of the river can be swift with some whitewater sections. They stock the river with rainbow trout in the winter. There are numerous free entry and exit points during the winter now. During the summer, these are commercial properties, and normally filled with party goers. You will need two cars to shoot the river yourself. There are also numerous guide services for raft trips. This is a world class river with spectacular scenery. It’s my favorite spot in all of the Texas Hill Country.