Abstract: An underwater marine protection system for preventing or retarding marine growth on vessels, pilings and submerged structures, in which a boat slip, or the like, has a series of gas diffusers placed under water located to direct gas towards the bottom of a marine vessel. The gas diffusers are connected to an ozone source for directing ozone gas through the diffusers towards the bottom of a boat. Skirts or curtains are connected to the pilings in the boat slip to prevent the free flow of water into and out of the slip where the water has been treated. A special top extends across the slip and around a vessel therein to increase the effectiveness of the ozone. An alternate embodiment has the gas diffusers formed in the bottom of the boat or submarine structure.