A crew member on a research vessel on a trip studying bioluminescence in the Gulf of Mexico filmed what appears to be a USO.

Here is his testimony: Before you read: I understand this is not technically a “UFO”, because it was seen in the water.

I work on a research vessel. Recently we had a trip, studying bioluminescence in the Gulf of Mexico. Around 2345, we were conducting research as normal, when a science party member saw a strange light about a quarter mile off our stern.
We immediately started to make way towards the light. The intensity of the light was quite astonishing, nobody in the crew or the science party knew what to make of it. At first, we thought it could have been a sunken vessel, or a navigation buoy of some kind that sunk.

We proceeded to get as close as possible to the light, and eventually we hovered directly on top of it. Our vessel has a moonpool in the center, which the crew and science party were able to carefully observe the light from directly on top.
We used a sub-surface camera to attempt and capture what the object may have been. The science party onboard automatically ruled out the light being produced by bioluminescent phytoplankton.