Luxcore is a pretty awesome for working on underwater scenes. Although in can be a bit tricky, I think you can get some really great results! If you want to know more about LuxCore and underwater scenes, I have some tutorials on my YouTube channel. Otherwise, enjoy these compositions!
Underwater Tutorial: https://youtu.be/-FDEBxRZelg
LuxCore: https://youtu.be/VRuCReoKrDI
Project Download: https://djtutorials.gumroad.com/l/zfklpe