Remote rivers in Alaska suddenly turn orange

Dozens of streams and rivers in Alaska that were previously crystal clear blue are now suddenly murky orange. And that worries researchers.

It is a somewhat strange sight: orange colored rivers. It was researcher Jon O’Donnell who first noticed this striking phenomenon in 2018, when he visited a river that had suddenly turned a ‘rusty’ color, while it had been clear the year before. O’Donnell decided to inspect several waters using a helicopter. “The more we flew around, the more orange rivers and streams we discovered,” he says. “Some of those spots almost looked like cloudy orange juice.”

The researchers came across dozens of remote streams and rivers in Alaska that were previously crystal clear blue, but suddenly turned murky orange. “The size of the colored rivers is so large that they are even visible from space,” says researcher Brett Poulin. “They must be significantly colored to be observable at that scale.”

An aerial view of the Kutuk River in Alaska’s Gates of the Arctic National Park, which looks like orange paint mixing with the clear blue water. Image: Ken Hill / National Park Service

The research team is still in the dark about the exact cause. But there is no doubt that it worries them. As the climate changes, these degraded rivers and streams could have significant impacts on both drinking water supplies and fisheries in Arctic watersheds, the researchers say. “These orange-colored streams can cause problems, both due to toxicity and because they can hinder the migration of fish to their spawning grounds.”

Poulin initially compared the discoloration to the effects of acid mine drainage. The strange thing is that there are no mines near the affected rivers. One possible explanation is that permafrost, which is essentially frozen ground, retains minerals. As the climate warms, the metals that were previously trapped can be exposed to water and oxygen, leading to the release of acids and metals. “Chemistry tells us that minerals are weathering,” Poulin said. “Analyzing the composition of the water gives us an idea of ​​what took place.”

To analyze the composition of the water, the researchers collected for the study, which in Nature journal Communications: Earth and Environment has been published, several samples. In some samples of the affected water a pH of 2.3 has been measured, while the average pH of these rivers is 8. This indicates that the sulfide minerals are dissolving, making conditions highly acidic and corrosive and releasing additional metals. The researchers also detected increased levels of iron, zinc, nickel, copper and cadmium. “We see many different types of metals in these waters,” explains researcher Taylor Evinger. “One of the most dominant metals is iron. That causes the color change.”

Satellite images
Although O’Donnell first noticed the color change in 2018, satellite images show that the first rivers turned orange as early as 2008. “The problem is gradually spreading from small sources to larger rivers,” he says. “It is important that we can understand new problems or threats as they arise.”

Research into the mysterious phenomenon continues. Ultimately, the team hopes to understand what exactly happened to the water. In addition, they want to model potential risk areas and evaluate the impact on drinking water and fish stocks. And they think that is very important. The problem is spreading and impacting habitat, water quality and other ecological systems, turning once healthy areas into degraded habitats with fewer fish and invertebrates. And in some areas, rural communities depend on rivers for drinking water. In that case it may be necessary to purify the rivers. It can also affect the fish populations that provide food for local residents.

Can the tide be turned?
It is currently still uncertain whether the tide can be turned. “If global temperatures continue to rise, it is reasonable to assume that permafrost will continue to melt,” O’Donnell explains. “It is therefore very likely that rivers containing such minerals will turn orange and suffer a deterioration in water quality.”

More research will need to be conducted to gain a deeper understanding of the problem and to determine whether rivers and streams can recover, perhaps with the help of cold weather that promotes permafrost recovery. “I expect there will be much more detailed research to address some of the uncertainties we currently face,” concludes O’Donnell.