I would say forget it in this stage.
I am not a good videographer, but shoot pictures under water on a high level. I do both for fun. My photocamera is more or less on a pro level, but also for video I can shoot in 4k, but it is not a pro level. But for wide angle good enough to show on television.
I have shot 2 times for TV, and this was done with a gopro. Needed were some shots to show how icediving looks like and as instroduction for searching under water for missing people. I was not paid, it was voluntary.
For the icediving, I organised an event and it was seen by some reporters that wanted to come to make a short (5 minutes) documentary about it. The other time, I was somewere to look for missing people (also a voluntary thing) and this cold case got a lot in the news again. So they came and asked me if I could make some shots under water to show how it looks like what we were doing. The viz ended within 1 minute in zero, so end of shots, haha.
So for short presentations, they can find enough divers who want to take some video under water. And even a gopro is good enough for wide angle.
For photo you see the same, a lot of people are shooting and if they want to use a picture, most give them away for free. I have had publications in several countries, 2 of my pictures are now in a museum, pictures have been used in expositions, but I never got paid. I am now on a level that I have refused use of some pictures in a book and on a particular website, but that book and website are filled with other free pictures. Even if the quality is a little bit worser, free means better than pay for them.
The documentary part, a real documentary means a long period of work. And a lot of materials. Again the wide angle in clear waters is not that hard. But the macro is way much more work. No shadows, stable images (so use a camera on the ground, or use sometimes a fish in an aquarium), etc.
Only a few people in the world earn their money with this work. In 2014, there was a television channel that was looking for an underwater cineast. I believe it was based in the UK. People from all over the world reacted to this advertisement.
Some more earn some money with youtube. So this is were I would start with. And remember, to earn money here, you must be lucky.
Some of my friends shoot footage for some documentaries under water. They all do it as a side job. They get some money for the shots and do the editting also themselves, but it is not enough to make a good live from. Making a documentary takes sometimes up to 2 years. They need the seasons, etc. Most times they have an idea, look for sponsors, get the sponsors and make the documentation.
Also voices are not free. I use most times myself, but my voice is not the best one for serious documentaries. For one of my next videos I am afraid I have to pay for a voice also. But this also means, shooting video, make an edit, you still have to think about voices and most times you cannot do that yourself.
