During the take-off run, the aircraft struck an unseen, submerged object. The impact launched the aircraft out of the water prematurely. The pilot placed the aircraft back on the surface of the water and continued the take-off run. The pilot then noticed that water was entering the cabin behind the front seats and that the aircraft began to vibrate. He rejected the takeoff and stopped the engine before evacuating his passengers and himself. The aircraft sank approximately 15 minutes later.