El Hierro has no sandy beaches to speak of. The coast is almost entirely volcanic rock, and the swimming is done in natural pools and small coves carved from the lava.
Tamaduste is the most popular spot, a natural lava pool on the northeast coast that opens to the sea — sheltered enough for children and snorkelling, with clear water over a rocky bottom. It's a short drive from Valverde.
Charco Azul on the north coast is a similar arrangement — a series of rock pools separated from the open ocean by a natural wall, calm and clear in most conditions. The pools warm up nicely by mid-afternoon.
La Caleta near La Frontera has a small pebbly cove and is the main swimming spot on the western side of the island. The water here is some of the warmest, sheltered by the El Golfo headland.
The diving and snorkelling around El Hierro is exceptional — visibility regularly exceeds 30 metres in the Marine Reserve, and the underwater volcanic terrain hosts excellent marine life including grouper, rays, and barracuda. Several species of rare beaked whale inhabit the deep water around the island.