The Amazon River is known for many things, but massive coral reefs were never one of them until now. According to a report from the Los Angeles Times, a team of scientists has discovered a huge reef system right near the mouth of the river.

Scientists published their findings in the journal Science Advances. The study offers new insight into how coral could make such a massive colony in an ecosystem previously thought inhospitable to the creatures.

Coral reefs are made of massive series of individual little animals, which are related to anemones and jellyfish. Together, these little critters’ exoskeletons create massive reefs that can stretch for thousands of miles. Coral reefs serve as an important shelter for all types of marine life, including fish, arthropods and reptiles.

The finding was particularly shocking because coral typically only grows in clear tropical waters. The Amazon’s water is rich with sediment and murky, which blocks sunlight from penetrating and supporting the food web on which coral relies.

Study co-author Patricia Yager, an oceanographer from the University of Georgia initially set out to study the sediments that were deposited into the ocean at the Amazon’s mouth, but her research took a left turn when a colleague dug up an old paper from the 1970s that reported a reef fish being caught in the area – an unusual occurrence.

Wanting to investigate further, the team began sending radar signals to the bottom near the mouth of the Amazon River. After finding something that could have plausibly been coral, the scientists dropped a dredge in the water to pick up samples.

“Unbelievably, we brought up on board the deck just the most amazing things I’d ever seen… beautiful, colorful coral reef animals that I had no idea were down there,” said Yager.

The coral reef at the mouth of the Amazon River is an amazing discovery, but it’s already under threat by fossil fuel interests in the area. According to the study’s authors, “In the past decade, a total of 80 exploratory blocks have been acquired for oil drilling in the study region, 20 of which are already producing. These blocks will soon be producing oil in close proximity to the reefs, but the environmental baseline compiled by the companies and the Brazilian government is still incipient and largely based on sparse museum specimens.”

A press release from the University of Georgia describing the details of the study can be found here.