Cited as one of the nation's cleanest lakes, Lake Ouachita (pronounced WA-shu-ta) is a 40,000-acre lake surrounded by forests and mountains. Just a few minutes from Hot Springs, Arkansas, it's a popular spot for swimming, skiing, scuba diving, boating, and fishing. There are RV sites and cabins available for camping.
If you go:
The park is open all day, year-round, and there is no fee to enter the park or swim. Note that as of this writing, some sections may be closed due to recent tornado damage. Boat and kayak tours are available, and various types of boats and equipment are available for rental.
Links:

5451 Mountain Pine
Mountain Pine, Arkansas 71956 USA
lakeouachita@arkansas.com
Phone Numbers:
Park Office
+1 (501) 767-9366
+1 (501) 767-9366