Dana Peak, on Comanche Gap Road off of FM 2410, and Stillhouse Park, on Simmons Road off of TX 190, are the best bets for swimming. The lake has an irregular shape and rocky, chalky shores. The little town of Salado hosts the only spring-fed watering hole in the area. Salado, which means 'salty', is an old Tawakoni Indian settlement. It was settled in 1851 and became a well-known stage stop on the Chisholm Trail.
Today there is a large, wide swimming hole behind a dam located downtown.
Finally, there are a number of access points to the Colorado River east of Longhorn Dam in Austin. The river, of course, empties into the Gulf of Mexico and there are numerous parks the whole length. The river here is wide and has a slow current and the riverbed is mostly sand and gravel. When you get to downtown Bastrop, check out Fisherman's Park on the banks of the Colorado River. The Iron Bridge spanning the river is historic and has been integrated into the park with picnic tables, benches and a walkway across the water.