A reef discovered at the mouth of the Amazon River is muddying scientists’ conceptions of those rare underwater communities.

On April 22, a team of Brazilian and American scientists published an article in the journal Science Advances detailing their discovery.

The reef covers around 3,200 square miles and stretches from the French Guiana border to Brazil’s Maranhao State. That is an area larger than the state of Delaware.

“This is something totally new and different from what is present in any other part of the globe,” Fabiano Thompson, an oceanographer at the Universidade Federal do Rio de Janeiro and a member of the study, told the Smithsonian Magazine. “But until now, it’s been almost completely overlooked.”

What makes this reef so unique is the type of water in which it thrives. Most coral reefs thrive best in sunlit and clear saltwater (think of the Great Barrier Reef off the coast of Australia). The Amazon plume, which is the source of 20 percent of the world’s river-to-ocean discharge, does not fit that ideal picture.

“You wouldn’t expect to have gigantic reefs there, because the water is full of sediment and there’s nearly no light or oxygen,” Thomson told the Smithsonian.

Even so, this newly discovered system contains over 73 species of fish, 60 species of sponges, spiny lobsters and other reef-dwelling organisms. Twenty-nine of the collected sponges remain unidentified, potentially constituting new species, the study suggests.

This research can provide important insights into the influence of “suboptimal” habitat conditions on coral reefs and reef building.

“The paper is not just about the reef itself, but about how the reef community changes as you travel north along the shelf break, in response to how much light it gets seasonally by the movement of the plume,” Patricia Yager, associate professor of Marine Sciences at UGA, said in a statement.

Though this reef thrives in an unlikely habitat, the Amazon’s muddy water may have an effect on the reef’s biodiversity. This new reef has lower biodiversity than the Great Barrier Reef and other traditional coral reefs, which are home to a quarter of all marine species.

Before this research, very little of the reef had been mapped, largely due to its depth: the reef ranges from depths of 160 to over 320 feet under rough seas.

“Only 0.001 percent of the total area was covered, because people had only sampled a few points,” Thompson told the Smithsonian.

The researchers began mapping the reef in late 2012, taking surveys of the system. They used sonar instruments for mapping, and metal dredges and trawls to collect samples. The team went on a second mission in 2014.

The metal tools were destructive but necessary for these initial surveys. In the future, Thompson and the team hopes to use remotely operated vehicles equipped with cameras and lights.

Due to the lack of study on the reef and to its unique character, the researchers believe the reef warrants protection. They also argue that the reef probably contributes to sustaining fisheries that local communities depend on.

However, the reef has an uncertain future, as major oil and gas companies are exploring nearby areas for drilling. It is unclear how much damage the drilling, as well as continued fishing in the area, may cause the reef.

“Isn’t that always the case?” Yager told the Los Angeles Times. “You don’t know what you’ve got until it’s gone.”