When the pilot arrived at the airport, the top surfaces of the aircraft were covered with about two inches of snow. He stated that his preflight included a complete removal of the snow. However, he also stated that during the takeoff roll, there was a layer of snow grains, one-grain thick, sparsely covering the wing area. The takeoff was started on a runway covered with 1/4 to 1/2 inch of slush. During the takeoff roll, the pilot noted that the acceleration was slower than normal and the snow grains were staying on the wings. He rotated at 65 knots, but the plane did not lift-off at the normal speed. He decided to abort, but was unable to stop on the remaining runway. He stated that the wheels were hydroplaning. The plane momentarily left the ground as it continued over a drop-off at the end of the runway. The nose strut collapsed as the plane touched down in muddy terrain about 20 ft from a pond. The plane continued into the pond and came to rest in shallow water.