Two of the most popular start points are Pramuka Island and Tidung Island. From there, you can rent snorkeling gears for as low as Rp 30,000, and hire a boat (can be filled up to 15-20 people).
Sources and licences
Guide text adapted from the Wikivoyage article "Thousand Islands (Indonesia)" by its contributors, available under CC BY-SA 4.0. Read on Wikivoyage · Contributors · CC BY-SA 4.0