FAST FACTS
Where is it? Bartica, Guyana (6.4073096658, -58.62373473)
What is in the picture? A trio of waterways that merge into a striking ‘half-and-half’ river
Which satellite took the picture? Landsat 8
When was it taken? 16 August 2023
This striking satellite image shows the contrasting colors at the point where three rivers converge in Guyana. The multicolored waterways are a result of the country’s unique geology, as well as an increasingly disturbing human-made factor.
This unique hydrology is associated with the Guyana Shield, a 1.7 billion-year-old geological feature that covers Guyana as well as parts of Venezuela, Brazil, Suriname and French Guiana. The shield contains hard crystalline bedrock made of rocks such as gneiss and granite, meaning it is not easily eroded except by running water, which has carved many routes through the region.
In this photo, two smaller rivers – the Cuyuni River (left) and the Mazaruni River (middle left) – come together shortly before merging with the Essequibo River (middle right) to form one of Guyana’s largest waterways.
The town of Bartica, home to about 15,000 people, is located on the strip of land that juts out into the water at the secondary confluence. From there, the widened Essequibo River flows north for around 50 kilometers, before it flows into the Atlantic Ocean.
Before the merger, Mazaruni and Essequibo are dark brown, which is probably the result of tannins – chemicals released by decaying vegetation that stains waterways via a process similar to tea brewing. Cuyuni is light brown due to high levels of suspended sediment in the water, according to the Earth Observatory.
When the rivers meet, the lighter and darker waters do not mix easily because of the differences in density caused by varying levels of sediment.
While the presence of tannins is a natural phenomenon triggered by flooding, the high levels of sediment are the result of mining waste dumped in Mazaruni.
“This photo is from a wet time of year when all three rivers were running high and carrying a lot of sediment,” Evan Dethiera hydrologist at Colby College in Maine told the Earth Observatory. “But Cuyuni is the clear outlier, which we can attribute to the intensity of upstream mining.”
Guyana is a mining hotspot, mainly due to its vast deposits of gold, diamonds and bauxite, as well as lithium, copper and nickel, which are also associated with the Guyana Shield, according to US Department of Commerce.
The country’s mining industry first started in the mid-2000s, and since then the concentration of sediment in Cuyuni has probably increased tenfold, Dethier said. Similar changes have been documented in rivers across the planet.
ONE 2022 study led by Dethier revealed that sediment concentrations in Southern Hemisphere rivers have increased by around 40%, mainly due to mining and deforestation. However, the opposite is true in the Northern Hemisphere due to the construction of large dams, which have blocked the sediment flow by around half.
The changes in the global sediment flow may also affect the marine environment, because the sediment supply in most of the world’s oceans has changed drastically, the study warned – but it is still too early to see what kind of long-term effect this may have.
An astronaut image from 2023 shows the moment the Alabama River briefly transformed into a billowing golden snake, similar to the shape of a Chinese dragon.
