We've got it good now with small, light, waterproof cameras. I remember back in the late 90s, early 2000s, I needed to shoot some underwater video in one of the local rivers. I couldn't afford a video camera and an underwater housing, and a set of U/W lights. I could, however, afford a small (at the time) 8mm digital tape video camera. I picked up some 6" PVC pipe, and some fittings and made a housing. It was just a little too big for 4" PVC. The housing was enormous, and I had to weight it down with it's own weight belt to make it neutral buoyancy. You started the camera on the boat, put it in the housing and hit the water. You had a lot of extraneous footage to edit out, but it worked. I took two large dive lights, and made a mount bar and some diffusers to get even light coverage.
Now, a couple hundred dollar Go Pro will get you HD video as deep as I want to dive. And the whole thing will fit in the palm of your hand, minus the lights.
I still have the video of the 4 thousand year old Native American canoe a buddy and I found in a local river. Plus I had a blast thinking through the process of making the housing.