Alaska's orange rivers more toxic than mine waste, study finds

The orange colour creeping through some of Alaska’s rivers is more than an unusual change in appearance; it is a sign that the chemistry of the water is changing too. The phenomenon first caught scientists’ attention in 2018, when once-clear streams in Alaska’s Brooks Range began showing striking orange and rust-coloured sections. Many of the affected waterways are in remote areas, far from the kind of industrial activity normally associated with polluted rivers. As permafrost thaws, water can move deeper into the ground and interact with minerals that were previously less exposed to flowing water, releasing acidity and metals. A new study published in AGU Advances has now examined six watersheds to understand what is happening to the water and how far the changes can spread.Orange water, but a much bigger change underneathThe rusty colour is produced when iron released through these mineral-weathering reactions oxidises, forming orange-coloured deposits.