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.
Website: www.ccrov.com

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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.

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Sublue

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).
Website: www.sublue.cn

Fig. 5: The Sublue booth.	Fig. 6: “Whiteshark Mini” ROVs.	Fig. 7: The “Whiteshark Max”.
Fig. 8: The “Whiteshark Pro”.	Fig. 9: The “Whiteshark Mix” underwater scooter (front) & another unknown model.