Lake travis is about 20 miles west of Austin. It was created by damming th elower colorado river. It is very large, and had a depth of about 150 feet. You can rent boats, scuba dive, swim and water ski. There are 3 main places to dive. Mansfield scuba park, windy point, and volente. You can get info from the lcra web site. There are also picnic and camping sites. hippie Hollow is divable, and it is the only nude beach in the area.
Equipment: I only patronize austin aqua sports. www.austinaquasports.com
Skydive san marcos - you can learn to go skydiving and skydive for fun for reasonable prices. it's about 40 minutes south of austin, but the staff is experienced, and the operation is well run.
Equipment: You need to make reservations first
Rowing, in a Scull. Since it never gets cold enough to freeze the river, you can rent a scull and row on it. There are also canoe and kayak rentals. IT's a nice way to travel up and down the length of the city, and see some terrific views. Don't get too close to the dam though, there is a lot of current next to the power plant. You can row from holly street (the downriver dam) all the way to redbud before you enocounter the upriver (redbud) dam
Equipment: Austin rowing club, texas rowing, boat rentals in the phone book. There are a few.