This is the best coral around Koh Tao.
I visited on a Snorkel Excursion, but you could easily swim out from the beach.
To get to the 'good' location from the beach, swim out to the right and follow the shoreline - the reef hugs the coast.
It is a bit of a swim, but the excellent coral makes it worthwhile.
This was my third visit to Koh Tao, and I had snorkelled at many locations around the island before, however I have to admit that I was surprised at just how good the coral was here. Also saw some large Black Tip Reef Sharks here as well as all of the other pretty reef fish that you expect to see.
Myanmar to New Guinea