The world’s deepest blue hole (marine sinkhole) lies off the coast of Mexico’s Yucatán Peninsula. It’s at least 420m (1,378ft) deep, but explorers still haven’t found its bottom.
Known as Taam Ja’, or ‘deep water’ in the Mayan language, it was discovered more than 20 years ago by a local diver, but it wasn’t until 2021 that scientists attempted to measure its depth. Using an echo sounder to bounce sound waves off the bottom of the hole, they estimated Taam Ja’ was 275m (902ft) deep. But another expedition in 2023 used a device called a conductivity, temperature and depth (CTD) profiler, with sensors that measure water pressure, to estimate its depth. This returned a reading of 420m (1,378ft), but they’re not sure it reached the bottom.