The water quality in major U.S. harbors has improved drastically over the last 15 years thanks primarily to the strict standards established by the federal Clean Water Act of 1972. An unfortunate by-product of that effort, however, is the resurgence of micro-organisms that feed upon submerged wood, commonly called marine borers. These creatures have caused the collapse of dozens of piers in New York Harbor, as well as marine structures on other waterfronts.
Two types of marine borers are responsible for most damage. Limnoria are shrimp-like crustaceans that swarm around piles of wood and eat it from the outside, leaving a distinctive hourglass-shaped pile. The teredo, or shipworm, bores pinholes on the outside a pile and proceeds to grow inside along the length of the pile, with the grain of the wood. A wood pile can be completely infected with shipworms and not be detected from the outside by an untrained eye.