Mr Lindberg said it was large and about 60ft in diameter and clearly visible on the sea bed.
'You see a lot of weird stuff in this job, but during my 18 years as a professional I have never seen anything like this. The shape is completely round,' he said.
He added that the scars on the earth surrounding it could show where the craft landed and skidded along.
Now, however, his team do not have the money or resources to examine the shape further.
If it does turn out to be a UFO it will be priceless, but if it is just a shape, it will be worthless.