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Summary: A team of scientists went on an expedition to a river in Alaska to find out why the river suddenly turned bright orange.

Abstract: The Salmon River in Alaska’s Kobuk Valley National Park is wild and scenic. Recently, scientists were surprised to find many of the streams in the park turning a bright, rusty shade of orange. What could cause such a change? One possibility is thawing permafrost. Permafrost is ground that normally stays frozen all year long. When it thaws, water can reach rocks that were inaccessible in the frozen ground for thousands of years. The water reacts with minerals in the rocks, making acid. The acidic groundwater carries certain metals, like iron, to streams. We traveled to the headwaters of the Salmon River and rafted down the river. We took measurements along the way. Our data showed that the water quality has become worse since the streams turned orange. We found toxic levels of iron, aluminum, and cadmium in the water. This may be to blame for the lower numbers of salmon returning to the area in recent years.

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