Lake Erie, the recreational front yard of Buffalo, Cleveland, Toledo, and Detroit, is gone. Though it supplies water for ten million people, even the heart of it has none of the dissolved oxygen necessary for the fish, plants, and insects on which lakes thrive. Erie now supports little aquatic life except trash fish, bloodworms, sludgeworms, and bloodsuckers. A monstrous cancer-like growth of algae, nourished by phosphates from industrial wastes, possesses this body of water.

Lake Erie is shallow, and some think that at the present rate it will be completely polluted with sludge, algae, and other deposits within twenty-five years.

Why? A river often washes and restores itself, but a lake is a bathtub that can be defiled by man to the point of becoming an open sewer.

Q. Underline a metaphor in the selection.