If you come to Mavrovouni beach, windsurfing is a "must-do". If you don't have equipment there is a school near Gythion Bay that can arrange everything.
If you are fan of windsurfing then the specific beach is one of the best choices in Peloponnese. It is not crowded, it gives south or west wind, but in August you can plan on your board with meltemi.
Take your board and your sail and have fun!