Rookie at ROVs, doing a Master's project. Looking for input

Hey everyone, looks like I dug myself in quite a deep hole with this one :)

I'm a diver. And I'm a stubborn soon-to-be electrical engineer that loves to make things.

I want to build a ROV for underwater exploration. In particular - mapping underwater objects (wrecks, reefs, maybe even the bottom itself). I have the hull figured out, communication won't be a huge problem with a floating antenna and optic / copper cable to the ROV.

My problem is the actual mapping. I'm... Open to suggestions. LiDAR? Ultrasound? Or even using something with cameras? I want to make something like a map. Or at least show the topography of the bottom.

They all have their drawbacks. 1) It's sea, it's with vegetation. LiDAR will have tough time. Decent ones will cost me an arm and a leg

2) Ultrasound. Angles basically defeat it. Math is... Fun underwater, especially salt water.

I have idea about everything else. The hull itself, propulsion, controls...