An entrance to an alien base is being suggested as a possible explanation for a mysterious rotating island in swampy land near Buenos Aires, Argentina.

Given the name The Eye, the island is described as a circle of land, surrounded by a thin channel of water. The hole in which the island sits - within the surrounding marshland - is about 120 metres in diameter.

It is in the delta of the Parana River at coordinates 34°15'07.8"S, 58°49'47.4"W, which can be entered into Google Earth to show the location of the feature.

The thin ring of water around the island is said to be clear and cold, in contrast to all the swampy marshes surrounding the hole.

To find out more, the filmmakers who discovered the island have launched a crowd funding campaign on Kickstarter, wanting to raise US$50,000 (NZ$69,2781) to fund a scientific expedition to unravel the island's mysteries.

By Wednesday morning they were still short of US$5000 but have 40 days to go.

THE EYE The water around the island is unusually cold and clear.

Focusing on the alien base angle is not terribly fair to those behind the campaign. It's not their idea, rather it has come from a website called UFO Sightings Daily, which is unlikely to be the most unbiased of commentators.

Based on the accounts on the Kickstarter page, the island is easily strange enough without the alien angle thrown in.

The crowd funding site doesn't appear to touch on that possibility, but introducing the project Argentinian filmmaker Sergio Neuspiller does hint at the possibility of some unearthly origin.

GOOGLE EARTH The Eye is south of the Parana River, near Buenos Aires.

The island was found during pre-production work for a horror film in the area, supposedly based on real stories about UFOs, mysterious lights, extraterrestrials, ghostly creatures and other paranormal activity, he said.

Events in the stories happened in an area south of the Parana River, and it was in the middle of those locations that the team spotted the rotating island, while looking on Google Earth.

"We call it (dramatic pause) The Eye," Neuspiller said on a video, spooky music swelling in the background. In Spanish it is El Ojo.

THE EYE After fighting through swamp land for eight hours, the explorers finally reached the island.

Both the circular shape of the island and of the edges of the hole in which it sits were so perfect "it's hard to believe this a natural formation".

Using the time slider tool on Google Earth, it was possible to see the island had moved around within its hole since the first available picture in 2003.

Among the questions posed by the formation was why aquatic plants had not covered the island, given the lack of water currents, Neuspiller said.

The team had flown over the island and - on the second attempt - managed to fight through near impenetrable vegetation and swampland for eight hours to reach it.

"The place was amazing and extremely strange. We discovered that the water is incredibly clear and cold, something totally unusual in the area. The bottom is hard, in contrast to the swampy marshes surrounding it,' Neuspiller said.

"The centre parts floats. We don't know over what, but it floats."

Among others shown in footage on the Kickstarter page is Pablo Suarez, a researcher at Boston University.

"This business of The Eye is very, very intriguing," Suarez said.

"Basically we have an external perimeter that is constant in time, and it's almost circular, in a flood plain ... where things normally change and are muddy."

It did not seem to be some kind of crater or other typical natural phenomenon. The island inside the perimeter moved at times and sometimes became elliptical.

"What is going on and why, and what gave origin to this unusual feature?" Suarez said.

He hoped it might be possible to set up continual monitoring of the island from above, as well as putting instruments on the island, and having experts carry out research.