I had an opportunity to visit recently and I had a great time out on the lake. The staff was great and the rental equipment seemed to be in good shape. I had never been paddle boarding before, but it was a fun experience and I was say it takes some time to get use to it. This is also probably the best dock to go out in the lake if you want to see the bats under the Congress bridge.
If you are looking for S Congress Ave bridge bat watching tour, go no further. This place does not advertise much so might be difficult to find them when you search for bat tours. But this is one the most reasonable tour ($35) for two person kayak for almost 2.5 hours on the river. The guide (Kyle) was most helpful and gave us the best of time on the river. He took us to the best point to watch the bats which other high charging people would not. In total it was the best decision to go with them for bat watching. They do not have parking but you can 'pay to park' on trinity and walk to their shop in two minutes.
Wonderful view of Lake Austin, located right next to the Four Seasons hotel. If you're looking to rent a stand up paddle board or a kayak from South Congress Kayaks, wander down to the lakeside, where three public docks will give you direct access to the lake, right next to South Congress Bride. The staff is accommodating, though it can get crowded on Saturdays and Sundays. The cafe, housed in Waller Creek Boathouse as well, is wonderful for a quick bite to eat, a coffee, or a glass of wine after you've finished paddling out on the lake.