In a land airplane, determining takeoff direction is a relatively simple matter of finding a suitable runway with the most favorable wind, lining up with the centerline, then accelerating to rotation speed.
On water, pilots have many more factors to consider. In addition to wind direction, pilots must evaluate the shape and depth of the waterway, wave height, current, obstacles, traffic, and sun angle.
Once in position for takeoff (water rudders up, flaps set), the pilot’s task is to get over the “hump” and onto “the step” as quickly as possible to minimize hydrodynamic drag as the airplane accelerates. In most floatplanes, this means applying full engine power and full back elevator until the airplane rises over the hump, then releasing back-pressure (or even applying slight forward pressure) so that the floats plane efficiently across the water (like water skis) with as little water resistance as possible.
To further reduce surface friction, some pilots sharply apply ailerons to raise a float (usually the left float) out of the water. Doing so allows the airplane to accelerate to flying speed more quickly.
Once clear of the water, floatplane pilots tend to keep their airplanes in ground effect as they accelerate to their best climb speeds.