Rivers may appear to be shades of yellow, green, blue or brown; subtle environmental changes can alter their appearance.
This illustration depicts the rivers of the contiguous United States as they would look to the human eye (approximately). Note the dry west. Look at a large version!
About one-third of the large rivers in the continental United States have changed their dominant color over the past 35 years according to this research. About 56 percent of US rivers studied were dominantly yellow over the course of the investigation; 38 percent were dominantly green.
The most extreme color changes often occurred near man-made reservoirs.
The map was created from 234,727 images collected by Landsat satellites between 1984 and 2018. The data set includes 67,000 miles (100,000 kilometers) of waterways that are at least 200 feet (60 meters) wide.