If you are Super or Fiery Mario, you can pull this off in any water level. Stop right before the pipe in the water that takes you out to dry land somewhere. Press and hold Down to duck, then press A to swim. You can then let go of Down. As long as Mario's feet don't touch down anywhere, you'll notice that his head goes through to the top of blocks. Keep pounding Mario's head on the blocks as you swim above the exit pipe. Soon he will be pulled behind the pipe to the right side of the screen. The only way out of this is to reset the game, or wait for time to expire.