Crossing to Britain's Tidal Islands

There are few journeys quite like the walk to a tidal island. For a few hours each day, the sea draws back to reveal a path of sand, rock or ancient stone across which visitors can reach a piece of land that is otherwise cut off. Then, as the tide returns, the path disappears beneath the water and the island becomes an island once more. Britain has several dozen such places, ranging from tiny rocky outcrops to islands with villages, castles and churches, and they attract a growing number of tourists every year.

Tidal islands owe their existence to a particular combination of geography and tides. They usually lie close to the mainland, separated from it by shallow water, and are found on coasts where the difference between high and low tide is large. In some cases, the link to the mainland is a natural bar of sand or shingle built up by currents. In others, it is a man-made causeway, sometimes centuries old, constructed by monks, farmers or fishermen who needed a reliable way of crossing to the island on foot or with carts.

Many tidal islands have a long religious history. Early Christian communities were attracted by their isolation, which offered peace for prayer while still allowing contact with the outside world. The tide shaped the rhythm of daily life, deciding when supplies could be brought in and when pilgrims could arrive. On Carrick Holm, a small island off the south-west coast, the ruins of a medieval chapel still stand on the highest point, and a stone cross marks the spot where travellers once gave thanks for a safe crossing.

The islands are also important for wildlife. Because they are cut off for much of the day, they offer a refuge for nesting seabirds and seals, which are less likely to be disturbed than on mainland beaches. The surrounding mudflats and rock pools, exposed at low tide, support a rich variety of crabs, shellfish and seaweeds, and attract wading birds in large numbers. On some islands, parts of the shore are closed to visitors during the breeding season, and wardens patrol to make sure that dogs are kept on leads.

Today, the main visitors are tourists, and their numbers create challenges for the small communities who live on the islands. Owen Tregarth, who has worked as a warden on Carrick Holm for fifteen years, says that on a fine summer day more than two thousand people may cross the causeway, compared with a permanent population of fewer than forty. Visitors bring income for cafés and guest houses, but they also put pressure on narrow paths, fragile grassland and the island's limited supply of fresh water, which arrives by pipe from the mainland.

The greatest concern, however, is safety. Every year, coastguards are called out to rescue people who have misjudged the tide and become stranded on the causeway as the water rises. The sea often comes in faster than people expect, and on some crossings it arrives from both sides at once, cutting off the path in the middle. Tregarth says that many of those rescued had seen the warning signs but assumed they would have plenty of time, while others had relied on tide information that was out of date or meant for a different place.

Various measures have been introduced to reduce the risk. Tide tables are displayed on large boards at both ends of most causeways, and some islands now publish safe crossing times online and through mobile apps. Refuge towers, raised platforms on which stranded walkers can wait for rescue, have been built on several longer routes. On Carrick Holm, volunteers stand at the mainland end of the path during busy periods and advise people whether they have time to cross and return. Tregarth believes that talking to visitors face to face is more effective than any sign.

For residents, living with the tide is simply part of life. Children's school days, doctors' appointments and deliveries all have to be arranged around crossing times, and there are days in winter when storms make the path impassable. Yet few islanders would choose to live anywhere else. As one long-term resident puts it, the tide forces people to slow down and plan ahead, and that is a lesson visitors could usefully take home with them.