Jetty:

A pier or structure of stones, piles, that is projecting into the sea or other body of water to protect a harbor, and/or deflect the current.

jetty-image1.jpg

"Jetty Image." Jetty image. N.p., n.d. Web. 12 Apr. 2010. <www.globalsecurity.org/military/intro/images/jetty-image1.jpg>.
"define jetty." Dictionary.com. N.p., n.d. Web. 12 Apr. 2010. <http://dictionary.reference.com/browse/Jetty+>.