Did you know 12 countries have teamed up to let casual beachgoers cross borders without passports?

This little-known cross-border public initiative has turned ordinary coastal trips into unexpected global cultural exchanges over the past three years.

At first glance, the rule sounds too good to be true: if you are walking along a designated public intertidal zone, or tidal beach, on the border of two participating countries, you do not need a passport, visa or any pre-approval to step across the official national line and move freely within a 1-kilometer buffer zone on both sides of the shore. Launched in 2021 by 12 coastal nations including Norway, Costa Rica, Thailand, Senegal and Chile, the shared intertidal protection agreement started as a tiny, underpublicized cooperative program between local environmental teams, and did not draw widespread public attention until a group of backpackers posted their border-free beach walking footage on social media last year. Up to now, more than 270,000 ordinary people have joined the casual cross-border shore activities, ranging from shell collecting to bird watching, without going through regular immigration checkpoints.

The most popular shared tidal stretch is located on the unmarked coastal border between Thailand and Cambodia, where local communities used to host small unregulated market exchanges for coconuts, hand-woven mats and freshly caught seafood long before the official agreement was signed. Now that the 1-kilometer cross-border zone is fully legal, the weekend coastal market has grown to welcome more than 2,000 visitors every Saturday, many of whom travel across the tidal line with only a cloth shopping bag, no travel documents at all. Local volunteer teams print hand-drawn tide route maps for free, and remind visitors to check the daily high tide schedule before heading out, so that no one will get stuck in the rising water halfway while crossing the invisible national line. Many birding enthusiasts from around the world plan their whole vacation around this site, as they can walk across two countries in less than 20 minutes while tracking rare migratory shorebirds.

Few people know the program did not start as a tourism project, but as a joint effort to track the population change of the red knot, a small migratory shorebird that travels more than 15,000 kilometers every year from the Arctic Circle to the southern tip of South America. Before the agreement was launched, environmental researchers from different participating countries could not share real-time observation data smoothly, and their annual population surveys could only record less than 30% of the total red knot population passing through the coastal areas. After the teams opened the data submission platform to ordinary beachgoers and allowed casual cross-border movements in the tidal zones, they collected more than 120,000 public-submitted observation records in three years, three times the total data volume collected by official scientific expeditions in the decade before the program launched. The extra data boosted the accuracy of red knot population estimates from 62% to 94%, and helped the International Union for Conservation of Nature update the species’ protection status earlier this year.

In recent months, participating local communities have expanded the casual cross-border activities to cover more public welfare programs, including joint beach garbage cleaning, sea turtle release volunteer work, and native mangrove sapling planting events. Many neighboring border communities that had little non-official contact for decades now organize regular weekend get-togethers on the shared tidal beaches, with home-cooked seafood dishes from both sides of the border spread out on woven mats for everyone to share. Last year, a severe storm surge pushed tons of discarded fishing nets from one side of the border to the other, and more than 400 residents from both coastal areas showed up voluntarily to clean up the trash together, finishing the whole work in six hours, a task that local government teams had estimated would take three full days to complete.

Despite all the positive feedback, the program will not be expanded to most of the world’s land borders in the near future, for it has very strict access requirements: the shared tidal zone must have no strategic facilities, no commercial mining or development plans, and local communities on both sides must have a long history of peaceful non-political interactions. Environmental researchers estimate that less than 30 coastal cross-border stretches around the world meet all these standards, so no one can expect to walk across national lines freely on most of the world’s beaches in the next 10 years. Still, this small, low-profile experiment has shown that many of the seemingly rigid, impenetrable international borders can have warm, people-friendly flexible spaces that have nothing to do with formal diplomatic negotiations, and ordinary people’s shared love for nature can become one of the most gentle and effective bridges for cross-cultural connection.