Water pollution? How about flushing the bilges?

LNG would vaporize instantly at normal temps.  Most modern oil tankers have segregated ballast water tankage anyway.  LNG tankers are pretty special beasts.  I cannot imagine they ever allow salt water into the pressure/refrigerated tanks due to the materials and need to avoid corrosion.  Although you can have stowaway critters in ballast that is a problem for any and all ships.

LNG is some scary shit though if mishandled.  Those acetylene and propane tanks blowing off in St. Louis today would be like fireflys in comparison.

Still, those facilities can be operated safely same as nuke power plants.  I prefer to look at wind farms myself, but everything to do with energy has some tradeoff.