PMC Editing Wiki: ArmA 3 Tools, PMC Heightmap Clipper
Reads ASCII Grid heightmap ASC file and clips its elevations to fit arma3 ocean 0 meter system, ie fixes oceans.
ArmA 3 oceans start below 0 meter elevations, basically exact 0 meters is sort of bugged or at least it looks really ugly, you should never use precise 0 meters.
Read more about ArmA 3 water colors in PMC Editing Wiki