>(You'd probably just pump water from the Pacific at one end, then put it back in the Pacific at the other end.) You most certainly would not. Because the risk

>(You'd probably just pump water from the Pacific at one end, then put it back in the Pacific at the other end.) You most certainly would not. Because the risk of spreading invasive marine species the MARPOL convention doesn't allow it. This means ships have to gradually replace all their ballast water during a passage. Just don't repeat Cougar Ace's mistake: https://en.wikipedia.org/wiki/Cougar_Ace https://en.wikipedia.org/wiki/Cougar_Ace