Check out this test of the Nikon Keymission 360 (reviewed here) underwater. I'm not talking about a swimming pool either ;)
The test is by Young Jae Kim, who took her Keymission to a dive trip in Cebu, Philippines. AFAIK, the Keymission is currently the only 360 camera that can be used underwater without an external housing. It can be used to a depth of up to 30 meters.
The Keymission includes two lenses: a regular lens and an underwater lens. The regular lens can be used even underwater, up to 20 meters. However, the underwater lens is designed to correct for underwater refraction. On the other hand, when the underwater lens is used, a black band will appear on the stitch line.
|regular lens on the left, underwater lens on the right|
Here's Ms. Young's video:
For the first part of the video, Ms. Young used the underwater lens. At around 3 mins, she switches to the regular lens (although in different conditions).
Ms. Young will be posting more videos from the Keymission. You can subscribe to her YouTube channel to see more videos.