It is hard to believe but the world is running out of sand. Our insatiable appetite for the substance that makes everything from skyscrapers to smartphones has led to environmental destruction in countries like Cambodia, where there has been a long history of illegal sand mining along the Mekong river. We are in the rapidly developing city of Phnom Penh to hear from the people whose lives and livelihoods have been threatened by the struggle for sand. Those who have fished the river for decades are finding that their nets are empty as the sand miners move in. People living alongside the Mekong have seen their houses crumble into the water as the riverbanks collapse.