What happened
The helicopter lifted off from the helipad and executed a left pedal turn. During the initial phase of flight, the pilot assessed the wind conditions, believing the breeze was coming from the southwest. This assessment led the pilot to anticipate a crosswind takeoff profile. However, the actual atmospheric conditions involved a tailwind.
As the aircraft reached the end of the heliport platform, it was flying at a slow airspeed over water. Under these conditions, the helicopter settled into a nose-low attitude. The pilot was unable to arrest the descent rate. Consequently, the helicopter descended into the river below.