The Mutual UFO Network (MUFON) investigated reports that a triangular-shaped UFO was seen emerging from Green Bay near Little Suamico, in Wisconsin, before flying off.
US-based MUFON received a testimony from a witness to the alleged event.
The object was said to be 100 to 150 feet in length and was seen at 2.10am local time on November 28.
Green Bay is a sub-basin of Lake Michigan, at the mouth of the Fox River.
The case was investigated by Susan Birttnen of Wisconsin MUFON, but closed as an “unknown sighting”.
In a report, Ms Birttnen wrote: “He reports they witnessed a triangular-shaped object fly out of the water of Green Bay, traveling at approximately 35 knots.
“It was so close that they could hear a muffled jet sound. As it came out of the water it turned on its side as it traveled west and gained elevation.
“Based on the evidence and the data provided by the witness, I conclude that this case is in the unknown category.”
The witness, who has not been named by MUFON, the world’s biggest organisation dedicated to UFO research, provided a description of the object.
They said: “The colour was dark and it had blue flashing lights.
“The elevation was at 500 feet and the distance was less than 1,000 feet. The side of the triangle was between 100 to 150 feet.”
The witness has a theory that it may have been a top secret craft developed and operated by the US Air Force.
Conspiracy theorists claim the US has secret so-called “black projects” based in classified air bases like Area 51 in Nevada where secret technology is developed.
Some even believe that they use alleged recovered flying saucers to devise new spy craft technologies.
The witness added: “I believe they are investigating the saucers and the orbs in some joint effort.”