Scientists have found a huge coral reef in the Amazon River. The scientists were on an expedition to learn more about plumes. These are the areas where a river meets the sea, and the freshwater and saltwater mix. The reef covers an area of 5,800 square kilometres. It stretches from the French Guiana coast to the Brazilian rainforest. Reefs are rarely found in rivers because the water is usually too muddy. It also does not contain enough salt.

The scientists explored just 10 per cent of the reef. They found 73 species of reef fish, some carnivorous. They also found sponges, creatures and other marine life that had adapted to life in the dark water. A researcher said: "We brought up the most amazing and colorful animals I have ever seen." However, the area will be explored for oil. The researcher warned that the impact of ocean warming and oil exploration will put the whole system at risk.