Much of the dumping from ships is accepted as standard industry practice. To avoid capsizing at sea, for example, cruise ships, cargo carriers, and large tankers have weighed themselves down with ballast since time immemorial. These days, this ballast consists of millions of gallons of seawater that ships suck into their tanks on their way out of one port. Later, they pump it out halfway around the world as they approach the next port. Scientists now know, however, the ruinous effect of this practice on local habitats. This purged water carries invasive species like the zebra mussels that
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