It's not hard, seriously. You will just need a hidden item to move in front of your unit, towards the facing of your unit. You will check if the point at the item's position is water-filled ((Terrain pathing at (Point1) of type Floatability is off) Equal to False) {Point1 = (Position of item)} and you will also check for the terrain cliff level. If the terrain cliff level is Equal to 0 (this level is applied for the default cliff level the editor has, when it creates a default map) and your unit is moving (a library might be needed here, if you don't want clumsy effects with simple coding, although it can be done just fine), then change your units fly height, to support pathing in the deep water.