Manta rays in the Maldives: Hanifaru Bay and the other spots, month by month

Picture yourself floating face-down in a metre and a half of water, watching a line of shadows as wide as cars glide toward you. Not one, not two: a chain of manta rays barrel-rolling with mouths wide open, one behind the other, in a slow carousel that filters plankton from the water. Above you, below you, beside you. At Hanifaru Bay, on the right days, the mantas aren't a sighting: they're a phenomenon, and you're inside it.

Hanifaru Bay, in Baa Atoll, is one of very few places on earth where dozens (sometimes over a hundred) manta rays gather at once to feed. It's a small dead-end bay that works like a plankton trap: when the monsoon currents and full-moon tides concentrate the plankton inside it, the mantas arrive from across the atoll for the banquet. Occasionally, among them, a whale shark appears too. It's a UNESCO heritage site, and one of the most powerful wildlife experiences the Maldives can offer.

But there's a practical side the postcards don't show, and it's the one that separates the trip of a lifetime from an expensive disappointment: Hanifaru is seasonal, it's strictly regulated, and it's not the only place to see mantas. This guide tells you when to go, how the bay works, where else mantas can be found year-round, and why timing matters more than location.

Hanifaru is a tiny bay (a few hundred metres) on an uninhabited island in Baa Atoll. Its shape is its secret: it's an underwater cul-de-sac. When the southwest monsoon current pushes plankton-rich water against the atoll, and the tide funnels it into the bay, the plankton gets trapped and concentrates into a dense soup. For a manta, which filters water to live, it's an open-air buffet. And so they come: first a few, then dozens, on exceptional days more than a hundred.

The spectacle has precise names that biologists use to describe it. Cyclone feeding: dozens of mantas spiralling in a column, like a living tornado, each rolling on itself with its mouth open. Chain feeding: an orderly line, each one following the tail of the one ahead. It's hypnotic, and it's also silent: the only sound is you trying not to hold your breath in excitement. The Maldives is home to the largest known population of reef mantas in the world, and Hanifaru is its most famous stage.

"The first time at Hanifaru I stayed completely still, watching, and forgot to take a single photo. A three-metre manta passed so close above me that I saw my own reflection in its eye. You don't chase mantas: you stop, you become part of the water, and they decide to come to you. It's the only place where I felt like a guest, not a spectator." Samuele Arcolace, founder of Maldivando

Mantas don't keep a calendar: they keep an appetite. They move where the plankton is, and the plankton moves with the monsoons. During the southwest monsoon (roughly May to November) currents push nutrient-rich water against the eastern side of the atolls, and that's where Hanifaru sits. During the northeast monsoon (December to April) it reverses: the plankton concentrates on the western side, and the mantas migrate across. That's why Hanifaru has a precise season, while mantas in general can be seen all year: you just need to know which side to look on.

Hanifaru isn't a free beach where you jump in whenever you like. It's a Marine Protected Area within the UNESCO Biosphere Reserve of Baa Atoll, and access is regulated to shield the animals from tourism pressure. Scuba diving is banned: you enter only by snorkelling, from the surface. There's a ranger station that monitors access, a cap on how many people can be in the water at once, timed slots (usually around 45 minutes), and operators' boats must hold a permit. The rules may seem strict, but they're the reason the mantas keep coming back.

If your dates don't line up with Hanifaru's season, don't give up on mantas: change spot. Beyond feeding aggregations like Hanifaru, there are cleaning stations: reef points where mantas go to be cleaned by smaller fish that eat the parasites off their skin. There the mantas hover mid-water, calm, for minutes at a time: a different experience from Hanifaru (fewer numbers, more intimacy) and available almost all year, on one side or the other of the atolls depending on the monsoon.

Almost all the mantas you'll see in the Maldives are reef mantas (Manta alfredi): wingspan up to three or four metres, resident in the atolls, identifiable by the unique pattern of black spots on their belly: biologists ID them one by one from exactly that, like a fingerprint. Far rarer is the oceanic manta (Mobula birostris), which can exceed six or seven metres across: a giant of the open seas that occasionally turns up at the most exposed points. Both are utterly harmless: no sting, no teeth to fear, they filter plankton and nothing more. Swimming alongside them is as safe as it is unforgettable.

Hanifaru is uninhabited and protected: you can't sleep there. The classic base for the excursion is Dharavandhoo, the local island in Baa that hosts the atoll airport: convenient in season, but the transfer from Malé requires a domestic flight. If instead you want mantas without depending on Hanifaru's window, or combine them with whale sharks on the same trip, the most reliable choice is South Ari: cleaning stations most of the year and concentrated marine life. Here are three local islands, three different approaches.

Good news for those without a certification: diving isn't necessary for mantas, and at Hanifaru it's actually banned. The Hanifaru aggregation is experienced entirely by snorkelling, from the surface: in fact, it's the best way to take in the whole scene. At cleaning stations, some deep spots are for divers only, but many are shallow enough to enjoy perfectly well from the surface. If you can swim and use a mask and snorkel, you have access to ninety percent of manta experiences. A diving certification is a bonus, not a requirement.

Almost every manta disappointment comes from one misunderstanding: treating Hanifaru as a place you can visit at any time, rather than as a seasonal appointment with nature. Here are the most frequent mistakes.