Aitutaki, Cook Islands

Aitutaki is a triangular atoll 45 minutes north of Rarotonga by Air Rarotonga — a volcanic plug at its northwestern corner fringed by a wide shallow lagoon enclosed by a chain of islets (motus) running along the eastern and southern rim. The lagoon is roughly 50 square kilometres, almost entirely under 5 metres, and famously aquamarine over the white sand floor. One Foot Island (Tapuaetai) at the southeastern tip of the motu chain is the most photographed location in the Cook Islands. Tidal range at Aitutaki is in the same band as Rarotonga — mixed semidiurnal, 0.5 to 0.8 metres spring range. The significance of the tide here is in the shallow lagoon itself: at low water on springs, the sandbanks connecting the motus dry completely and the lagoon's inner shelf becomes a walkable sand flat. Boat tours from the main island crossing to One Foot Island time their runs around this: deep enough to motor at high water, too shallow on the inner sand flat at low water. The southern passage through the motu chain is the main tidal exchange point; current through the passage runs up to 1 knot at spring peak, fast enough to affect kayak crossings from the main island to the outer motus. Tide predictions for Aitutaki come from Open-Meteo Marine — accuracy ±45 minutes on timing, ±0.2 to 0.3 metres on height. Given the shallow lagoon environment, height accuracy has direct bearing on passage planning across the inner sand flats.