WITNESSES STATED THE AIRPLANE MADE TWO PASSES NEAR A MARINA AT APPROX 100 FT. ON THE SECOND PASS, FROM WEST TO EAST, THE AIRPLANE PULLED UP SHARPLY, AND THE ENGINE POWER WAS HEARD INCREASING. AT APPROX 400 FT, THE AIRCRAFT STALLED AND ENTERED A SPIN TO THE LEFT INTO THE WATER. PILOT'S TOXICOLOGICAL TESTS WERE POSITIVE; 0.002 UG/ML TETRAHYDROCANNABINOL CARBOXYLIC ACID (MARIJUANA) IN BLOOD.