For the past three years, the group has visited Memphis, Tennessee, each spring to help clean up a harbor on the Mississippi River where the waters are thick with debris.

CNN: Taking out the rivers' trash, one piece at a time

"It works on Boston Harbor water, on Charles River water, anything, " says Metcalfe.

FORBES: Cheap Hydrogen From Dirty Water...Maybe

Untreated sewage and the 1.3 million pounds of polychlorinated biphenyls that General Electric dumped in the Hudson River turned the harbor into a cesspool.

FORBES: Magazine Article