ARE aliens intent on invading the Great Barrier Reef?

A Cairns woman has photographed, what she believes, is a UFO flying off Fitzroy Island, while she was sailing back to the mainland from a reef fishing trip on Saturday afternoon.

Jenny Morrison was returning from Elford Reef, about 50km east of Cairns, after spending a day at sea with friends, and took a series of photographs of the sunset on her smartphone.

When she later examined the photos, she noticed in several of the images, an inexplicable luminous green dot shrouded in a distinctive flying saucer shape.

"There's this little light, that looks just like a bit of water on the lens," she said.

"I haven't edited the photos, or done anything to them.

"When you look through the photos, though, the dot is in the middle of a saucer-shaped shadow thing.

"I don't know how to explain it."

Adding to the mystery, the green dot eventually vanishes from the last few photographs in the series.

Ms Morrison said she did not notice anything with her naked eye, when she took the photos.

"It's so weird. It looks really real - like something you'd see on TV," she said.

"It's crazy."

Far North Queensland is considered a UFO hotspot, with several sightings of mystery aircraft in the sky over several decades.

The Cardwell UFO Festival, held each October, celebrates the region's interstellar links by inviting the public to share their experiences of the unexplained.