An orange tributary of the Kugororuk River in Alaska.Joshua Koch, US Geological SurveyScientists say that dozens of waterways in Alaska are "rusting," or turning into a dirty orange.They said permafrost thawing in the summer is now exposing minerals to the surface, releasing metals and acid.Some brooks and streams are turning so acidic that they're comparable to lemon or orange juice.At least 75 of Alaska's brooks and streams have been turning a dirty orange likely due to thawing permafrost, with some rivers so impacted that the discoloration can be seen via satellite, a new study says.This phenomenon, which researchers say comes amid unusually rapid warming in the region, was first observed in the northwestern state in 2018, scientists told Business Insider's Jenny McGrath in January.The researchers have been stumped by it for years.