If you've ever wanted to see large numbers of manta rays close-up, this is probably the best place in the world to do so. There are in fact three seperate sites here on the west coast of the island, the channel which is usually the starting point of the dive, Manta Ridge and Manta Ray Bay.
M'il Channel runs through the reef, varying in depth from 15-35m and slopes off into the depths. It is quite often a drift dive if the currents are favourable and other than the mantas, eagle rays, whitetip reef sharks, groupers and jacks are common.
As you drift through the channel, you will be surrounded by a dazzling array of hard and soft corals, including large tracts of leather coral and purple soft corals. On an incoming tide, the current will take you to a series of coral heads that are known as Manta Ridge. The best place to wait for and observe the mantas is here as you can take shelter behind the coral formations and see them approach this cleaning station where the wrasse clear them of parasites. The opportunities for photography are superb.
Slightly further north, the channel becomes deeper and the current less strong. It is here that you arrive at Manta Ray Bay. The bottom is sandy at about 20m and you can kneel on the bottom and interact with the mantas who use this site as another cleaning station. In addition to the wrasse, butterflyfish and angelfish help with the cleaning process.
The best time to visit these sites is between December and April. At other times of the year, the mantas migrate to Goofnow Channel on the eastern side of the island.