The colours of the rivers differ across the world. They might have shades of yellow, green, blue, or brown. Subtle changes in the environment can alter the colour of rivers, though, shifting them away from their typical hues. It is a usual process for rivers to change colours. It is explained by fluctuations in flow, concentrations of sediments, and the amount of dissolved organic matter or algae in the water. For example, yellow-tinted rivers are typically sediment-laden but low in algae. Blue water has little algae and sediment, while green water usually has algae as its dominant feature. New research shows the dominant colour has changed in about one-third of large rivers in the continental United States over the past 35 years. It is still unclear whether the colour changes are good or bad in terms of water quality. The next step is to investigate what humans are doing to cause those changes and whether it’s an improvement or degradation. Source: NASA Earth Observatory Images: 1. NASA/USGS Landsat; Geoscience Australia. Source: Landsat gallery 2. NASA. The images show colour changes from 1986 to 2020 along the Rio Grande River near the Elephant Butte Reservoir in New Mexico