El Ojo

Despite being one of the most popular tourist attractions in Argentina, the Paraná Delta is a vast area of 14,000 square kilometers, much of which remains largely untouched and unexplored by modern humans. Case in point, some of its greatest wonders have remained secrets until relatively recently, such as El Ojo ("The Eye"), just 50 km from Buenos Aires.

First brought to attention by a filmmaker on Google Maps, El Ojo consists of a 118-meter-wide floating circle of plants and mud in a slightly larger circular lake. Remarkably, photos over time show that the island, which has existed since at least 2003, appears to be gradually gyrating around the lake.

The mechanism by which the island formed and continues to move around remains unknown, due to a lack of study. Locals believed that it was the home of an ancient deity. A possibility, however, is that El Ojo is functionally similar to a floating ice disk found in the Presumpscot River in Maine. In it, a slow water current erodes away the surrounding ice to form a circle of ice inside a circular patch of melted water.