The Los Angeles Times has just run an excellent, if depressing, series called Altered Oceans. It details the tremendous environmental damage we have done to our oceans, some by greed, and some by carelessness, and some by accident. When I have a little more time I'd like to convert as much if the information as I can into a series of posts with placemarks. Until that time - at least until the LAT removes it from their website - you can find it at THIS LINK. There are excellent (flash presentation) photos, videos, and graphics.
The site may require (free) registration.

EDIT: The Los Angeles Times series Altered Oceans won a Pulitzer Prize for explanatory reporting on April 16, 2007 for this series.
EDIT: Here is a LINK to a post containing a graphic about Part 4 of this series.