@tmu Nice link
That technique is a lot more technical than my old school approach.
I still never finished my water level yet, because I got sidetracked to another project.
So, the fish are not swimming as they should yet, just on the screen for display while working on the graphics.
You will note that I used my splash to make the transition from above water to under water.
That was mainly just to exit the hot air balloon and put on the scuba gear.
I was still working on the physics for the swimming too, but that is really all there is to it, changing the characters movements to simulate the water drag/lag.
Coding things my way since 1981 -- Currently using AppGameKit V2 Tier 1