This UFO hovering over Glacier Bay in Alaska is being dismissed as an optical illusion

Staff at Alaska's Glacier Bay National Park and Preserve posted this remarkable video of a UFO, disguised as an island, hovering over the water. Of course, they'd have us believe that this is an astonishing example of a Fata Morgana mirage, but we know the truth. From their Facebook post:

When air of different densities meet, the air in Earth's atmosphere acts as a refracting lens, creating the mirage effect we see. Cool, calm air often forms at the water's surface- then, if warm dense air pushes down on the cool air at the surface, a lens is created. This phenomenon occurred on a warm day (70ºF+) in Glacier Bay, but is not exclusive to summer months.

Here are other images of floating spaceships that also have been dismissed as Fata Morgana: