There were quite a few companies promoting their UUVs (Unmanned Underwater Vehicles), also called ROVs (Remotely Operated Vehicles, undersea vehicles or submersibles. However, all the products I saw need to be controlled be a human operator. There were no AUVs (Autonomous Underwater Vehicles).
CCROV by Shenzhen Vxfly Intelligent Information Technology Co. Ltd
A low-cost, portable, remotely-operated underwater vehicle with a 4K camera and 100m diving depth.
Fifish P3 by Qysea
Another underwater photography drone. This one has a 162° wide FOV camera.
However, it looks like the tether cable just comes in coiled-up, which could get tangled easily.
This company has various, small ROVs for underwater photography.
With a big clear camera dome on front, they look like little futuristic submarines.
The camera is mounted on a gimbal and they come with a fancy-looking controller (see Fig. 7).