If Koh Tao is a divers mecca, then it's heaven for snorkellers. There are several excellent snorkelling spots on Koh Tao, both for experienced snorkellers and for people just wanting to try it out.

Rocky Bay in particular is famous for it's resident group of small (up to 2 meter) Blacktip Reef Sharks.

Mango Bay, Koh Nang Yuan and Aow Leuk are also top spots for easy snorkelling. A recently wrecked fishing boat in Lighthouse Bay is also worth a try.

Snorkelling is very accessible on Koh Tao. Most resorts rent out snorkelling gear on a pay per day basis. It not uncommon to pay as little as 100 Thai Baht for 24hrs rental. It's even better though, to buy your own gear - it'll save you a great deal of money in the long run and you won't have to bother with leaking masks or fins that give you blisters.