I did a little research on El Dorado in National Geographic after we read about it in Candide. The myth surfaced in the 16th and 17th century. All the rumors say tribes in the Andes mountains at Lake Guatavita would cover their new chieftains with dust and throw gold and precious jewels into the lake to an under water god. The Spaniards called the ruler El Dorado. A different tribe captured this area in the 14th century. Spaniards found many other places around the exterior of the region causing them to believe there was one area of concentrated gold. In 1545 they found the lake and tried to drain it. They found hundreds of pieces of gold but not the major treasure in the deeper water.
They even made a children’s movie about it that I used to watch when I was little.