April — the transition month: why 30 m visibility starts now

The southeast trade winds arrive in May. Before they do, in the three weeks either side of that transition, the Indian Ocean does something that even experienced divers struggle to describe without reaching for a superlative.

The northwest monsoon, which has been keeping the inner island waters warm, calm, and slightly turbid since November, begins to relax. The swell drops. The thermocline — the boundary layer between the warm surface water and the cold deep water — rises, bringing nutrients upward. Plankton blooms. And then, counterintuitively, as the plankton disperses in the strengthening current, the water clears.

At Shark Bank, twelve kilometres west of Mahé, April visibility averages between twenty-five and thirty metres. I have logged forty-metre visibility here in the second week of April on years when the transition was clean. You can see the seamount rising from 35 metres below as you descend, and the sharks — grey reefs, whitetips, the occasional hammerhead — circle the pinnacle in a way that is not threatening but is unmistakably purposeful.

April is also when the whale sharks arrive. They follow the tuna north from the equator, and they pass through the channel east of Mahé in the early morning, between 5:30 and 7am, before the day heats up and they sound to cooler water. The window is narrow. If you want to swim with a whale shark in the Seychelles — not a cage, not a tank, but the open ocean, with an animal the length of a school bus — you need to be in the water before the sun is fully up.

I have been guiding dives in these waters for fourteen years. April is the month I look forward to most. The water remembers something in that transition — a clarity that feels less like an optical condition and more like an instruction to pay attention.

*Dilo kler* — clear water. But here it means something larger than that.