The Penrhyn lagoon is the defining feature of the atoll — a vast enclosed body of clear water ringed by low coral islands. It is too large to see across in most directions, giving it the misleading feel of open sea. The lagoon supports rich populations of fish, sharks, rays, and sea turtles, largely undisturbed by fishing pressure.
Snorkelling and diving in the lagoon are exceptional for those with the equipment and the ability to arrange local transport to the better sites. Pearl farming has historically taken place in the lagoon, and black pearls from Penrhyn have a good reputation. Arranging access to the lagoon is done through local contacts — there is no commercial dive operation.