The Yukon River rises in British Columbia in Canada and flows through Yukon Territory before entering Alaska and finally draining into the Bering Sea. This image, recorded on 29 August 2017, shows how the river branches off into numerous channels that meander through the low-lying terrain on their way to the sea. The sandy colour of these channels and of the coastal water illustrates how much sediment the river carries to the sea at this time of year.

It is estimated that 95% of all sediment transported during an average year occurs between May and September. During the other seven months, concentrations of sediment and other water-quality constituents are low. However, scientists also believe that sediment flow has increased over the last few decades because permafrost is thawing in the Yukon River Basin and ice breakup occurs earlier in the year owing to warmer air temperatures. This is important because elevated concentrations can adversely affect aquatic life by obstructing fish gills, covering fish spawning sites, and altering habitat of bottom-dwelling organisms. Metals and organic contaminants also tend to absorb onto fine-grained sediment.

The Copernicus Sentinel-2 satellites each carry a high-resolution camera that images Earth’s surface in 13 spectral bands. While the mission is mostly used to track changes in the way land is being used and to monitor the health of our vegetation, it also provides information on the condition of coastal waters.