Inside most of the atolls is a complex formation of reefs. A number of these reefs are circular, enclosing a shallow lagoon, others irregular and shallowly submerged. All offer interesting and usually easy diving and excellent snorkelling. Some of the best diving is on submerged reefs called thilas; usually located in the middle of a channels, these rise from the atoll floor to within 10m (33ft) of the surface.
Scuba Diving in the Indian Ocean
Reef life is prolific, with over 700 common fish species and many more still to be discovered and classified; invertebrate species are reckoned to be in their tens of thousands. For the alert diver there are encounters with hundreds of species - from whale sharks and mantas to the smallest nudibranch - the Maldives has it all.
The southwest season
The diving on the west side of the atoll in the southwest season is spectacular. You will regularly encounter large schools of pelagic fish like sharks, eagle rays and tuna. Another noticeable feature of the southwest season is that the water temperature is usually one or two degrees lower that the usual 28º C (82ºF). This has an effect on both the behaviour and sightings of marine life, particularly the grey reef sharks and hammerheads , which seem to congregate in larger numbers and in shallower water at this time of year.
On the eastern side of the atolls, the southwest season is the best time to see manta rays and whale sharks. Here your visibility is not so good, but this is compensated for by the wonderful experience of diving with these huge plankton feeders.
The northeast season
This is the Maldivian summer. The effect of the season change on diving is dramatic. From November onwards the currents begin to flow from the northeast, visibility is superb and there is lots of action in the channels and thilas on the eastern side of the atolls from the sharks and other pelagic species. Currents tend to be stronger in January and then ease as we move into February. From February the waters calm down and the surface of the sea is undisturbed by any major wind or wave action. This continues through March and April with easy diving. The end of May generally sees the change of monsoon season back to the southwest.
Throughout the northeast season, pelagic species such as shark and jacks are to be found on the current points on the eastern side of the atoll. Manta rays and whale sharks, however, will only really be found on the west side during the northeast season.
Reference Scuba Tours Worldwide: http://www.scubascuba.com/maldives/diving