FIGURE 1. Chesapeake Bay, on the US East Coast, receives some ten billion litres of foreign ballast water each year.
From the following article:
Global spread of microorganisms by ships
Gregory M. Ruiz, Tonya K. Rawlings, Fred C. Dobbs, Lisa A. Drake, Timothy Mullady, Anwarul Huq and Rita R. Colwell
Nature 408, 49-50(2 November 2000)
doi:10.1038/35040695
Each litre typically contains about a billion bacteria and seven billion virus-like particles.
PAUL SOUDERS/TONY STONE