However...even though different scenarios...

A seaplane takes off either with the current, or against the current, it doesn't matter, as the friction of the water on the pontoons is not enough to overcome the thrust of the engines...regardless of flow direction.

Obviously, a tire rolls more easily than a pontoon floats, etc...especially initially, as the pontoon starts out sitting deeper, and is designed to plane up closer to the surface as speed increases.

So - until the CF's SEE that the tires don't turn UNLESS the plane moves forward...

....and that (AS the conveyor only MATCHES the speed of the plane) there is no such thing as rolling forward on the belt w/o forward motion RELATIVE TO THE BELT...

...as the ONLY thing that CAN make the tires TURN is a SPEED difference between the tire bottom, and the belt top.