Alaska's clear rivers turn orange. The causes hints at global warming

Transparent and clean rivers in Alaska are turning into rusty streams. Scientists are working on finding the answer to the cause of this phenomenon. The orange hue of the water, visible from space, is indeed alarming.

The once crystal-clear water flowing in numerous rivers and streams in Alaska is gradually changing its appearance. It is becoming increasingly murky, and its colour is turning rusty. Substances released into the water during the thawing of permafrost are suspected to be causing these changes.

A team of scientists from the United States Geological Survey, University of California, Davis, and other research centres has studied this phenomenon. They analysed rivers in Alaska that have started to change colour. This phenomenon involves previously extremely clear water bodies suddenly becoming murky and taking on a vivid rusty colour.

As part of the research, scientists collected water samples from 75 different locations spread out over an area the size of Texas (approximately 700,000 square kilometres or 270,000 square miles).

- The more we flew around, we started noticing more and more orange rivers and streams. There are certain sites that look almost like a milky orange juice – says one of the scientists, Jon O'Donnell, author of the study described in the magazine "Communications Earth & Environment".

There are concerns that the observed changes could signal water contamination with toxins harmful to both nature and humans. Additionally, murky water can hinder fish migration to spawning grounds. Dr O'Donnell noticed this problem when he visited one of the rivers in 2018. However, an analysis of satellite images showed that water discolouration has been occurring since 2008.

The researcher emphasizes that the river discolouration is so significant that it is noticeable from space. Therefore, the changes are notable.

The orange water resembles that which flows out of mines, but in the area where the research is conducted, there are no mines. Therefore, scientists have hypothesised that the colour change in the water is due to the permafrost thawing caused by climate change. Minerals released from the thawing permafrost change the water's colour.

Analysis of water samples showed that in discoloured rivers, acidity and concentrations of metals such as iron, zinc, nickel, copper, and even highly toxic cadmium have dramatically increased. The highest concentration is of iron, which is responsible for the change in water colour. According to the scientists, these changes are spreading gradually, from small streams to large rivers. The area where these changes are observed is constantly expanding.

To better understand what is happening in the rivers, scientists plan to conduct further studies. Researchers intend to conduct more investigations to clear up any doubts about the causes of this phenomenon.