Kaafu Atoll

Maldives

Mantas in the south-west monsoon from may until October but only with outgoing current !
Visibility will then not be so good because of all the organic debris.

Also white tips, turtles, Napoleon, snapper

From a liveaboard anchored in Himmafushi lagoon on the other side of from Severak dive schools with maximum of 1 hr with a Dhoni. 

Jump in at the gps coordinate, swim to deeper water (24 meter) then turn right and hold the reef on your right hand until you find some coli flower shaped rocks sticking out of the reef.

With the right current and season the manta rays will be there.

Lankan Manta Point