Paddy Sullivan is an ecologist, and every year he travels to the Brooks Range in northern Alaska to collect snowpack samples. The area he visits is remote and often inaccessible. The Salmon River, for example, is a place where bush planes rarely land. They’ll land outside of the watershed and then people walk in. Paddy’s been going here for 20 years now, and in that time he and Roman Dial — an adventurer and fellow scientist — have formed a hypothesis about why the area is changing so much: The retreat of sea ice fuels increasing snowfall and nearby landmasses, protects seedlings and improves soil nutrient availability. And all of this allows for shrubs to proliferate and trees to advance into the tundra. It’s called the Greening of the Arctic and it’s changing the land; It’s also changing how people and wildlife use the land.

In 2019, while Paddy and Roman were collecting their datasets they stumbled upon something concerning and out of place: The once gin-clear Salmon River had turned orange. They noticed other rivers and streams had turned orange as well. In all the years they’d been coming to the Brooks Range, they’d never seen anything like it. So, they decided that they needed to sound the alarm, to let other scientists know what was going on up there. And hopefully, with their help, they could figure out what the implications were for humans and the surrounding ecosystems. Because something like this — an occurrence that trickles down into other ecosystems — has the potential to trigger ecosystem collapse. This happens when the rules of an environment are altered in a way that forces wildlife and vegetation to change how they interact with their environment.