The Bali Sea Turtle Society is a conservation group working to protect olive ridley turtles. It's one of the more responsible turtle hatcheries in Bali, and re-releases turtle hatchlings into the ocean from Kuta Beach. Join the queue to collect your baby turtle in a small plastic water bath, pay a small donation, and join the group to release them. Signs offer excellent background info.
Stop by an hour before the release time to ensure activity is on for the day.