Abstract: A method to treat ballast water comprises injecting ozone into water loading into a sea faring vessel prior to charging the water into a ballast tank; and charging the ozone injected water into the ballast tank. A system for treating ballast water comprises a sea faring vessel including at least one ballast tank; an ozone generator that generates ozone, a ballast water conduit that uptakes water through a loading port of a sea faring vessel and conducts the water to load the ballast tank; and an ozone feed line that injects ozone from the generator into water in the conduit at an injection point located upstream to an intersection of the conduit with the ballast tank.