A team of scientists from Brazil and the United States discovered an enormous coral reef that stretches for some 600 miles. The reef is located at the mouth of the Amazon River, where the water is tainted due to the mixing of saltwater and fresh water. The reef system spans 3,600-square miles along the ocean floor, stretching from French Guiana to Brazil’s Maranhao state along the edge of South America’s continental shelf. The discovery of this reef is surprising due to the unfavorable conditions that are usually associated with large rivers such as salinity, pH, and light penetration, but it appears to be healthy.

“I kind of chuckled when Rodrigo first approached me about looking for reefs. I mean, it’s kind of dark, it’s muddy — it’s the Amazon River,” University of Georgia professor of marine sciences and oceanography Patricia Yager told The Atlantic’s Robinson Meyer.

The muddy waters at the mouth of the Amazon River are home to a big colony of sponges and other creatures that thrive in low-light waters, along with 73 different species of fish that were recorded in the survey. These discoveries were made by a team from researchers from the University of Georgia and the Federal University of Rio de Janeiro that were on an expedition to learn more about Amazon River Plumes, which are where the river’s freshwater mixes with the ocean’s saltwater, when they discovered the reef. Patricia Yager wanted to explore a continental shelf because of a scientific article from the 1970s that mentioned a scientist capturing reef fish along the continental shelf, which suggested that there may be a coral reef in the area.

“Our expedition into the Brazil Exclusive Economic Zone was primarily focused on sampling the mouth of the Amazon,” stated Yager.

The reef population varies along with water clarity, so the southern part of the reef, which gets more light, has a wide spectrum of reef critters. While further north, as the light diminishes, the wildlife transitions to creatures like sponges. Sadly, this incredible reef is at risk due to the offshore oil explorations and the human activities that are occurring near the reef. This reef contains some of the most colorful and beautiful organisms known to man, so lets keep it that way. It’s up to us to keep this reef in tact, along with the creatures that live there.

“We brought up the most amazing and colorful animals I had ever seen on an expedition,” Yager said.

This newly discovered Amazon coral reef is the 4th longest on Earth.  See list below of previous Top 10 longest coral reefs:

TOP 10 LONGEST CORAL REEFS ON EARTH:

1) Great Barrier Reef
Length: 1,553 miles (2,500 km)
Location: Coral Sea near Australia

2) Red Sea Coral Reef
Length: 1,180 miles (1,900 km)
Location: Red Sea near Israel, Egypt and Djibouti

3) New Caledonia Barrier Reef
Length: 932 miles (1,500 km)
Location: Pacific Ocean near New Caledonia

4) The Mesoamerican Barrier Reef
Length: 585 miles (943 km)
Location: Atlantic Ocean near Mexico, Belize, Guatemala and Honduras

5) Florida Reef
Length: 200 miles (322 km)
Location: Atlantic Ocean and Gulf of Mexico near Florida

6) Andros Coral Reef
Length: 124 miles (200 km)
Location: Bahamas between the islands of Andros and Nassau

7) Zhongsha Islands
Length: 50 miles (81 km)
Location: South China Sea

8) Saya Del Malha
Area: 15,444 square miles (40,000 sq km)
Location: Indian Ocean

9) Great Chagos Bank
Area: 4,633 square miles (12,000 sq km)
Location: The Maldives

10) Reed Bank
Area: 3,423 square miles (8,866 sq km)
Location: South China Sea, claimed by the Philippines