I picked up a Trident ROV Drone off Kickstarter, it has a few glitches but still been a pretty cool drone to play with when out on the water. Their is definitely a learning curve to orienting yourself, managing the tether and handling currents and drifting. They can go as deep as 300', so you are really seeing things no one has before. Unfortunately, they are discontinuing it and parts support will end this year, but there are a few Chinese companies making them now.
Here's a shot of Alaskan Shrimp in Prince William Sound, 300' down:
Here's a shot of Alaskan Shrimp in Prince William Sound, 300' down: