The Chesapeake Bay watershed dominates the lower left portion of the image, while snow and ice can be seen in parts of New England and Canada. The watershed or 165,000 square kilometer (64,000 square mile) drainage basin encompasses parts of New York (as far North as Cooperstown), Pennsylvania, Delaware, Maryland, Virginia, and West Virginia. The Chesapeake Bay (located at the bottom center of the image) is the largest estuary in North America and is an important fishery and recreation area. There are important linkages between the land surface upstream and the aquatic environment downstream: any activity that takes place with the Bay watershed impacts its water quality. One major environmental problem in the Bay is caused by excess nutrients, a process called “eutrophication”. Rainfall carries materials from the surface into the stream network of the watershed and ultimately into the Bay itself. Some of these materials, such as nitrogen and phosphorus, stimulate the growth of algae. When the algae die, they are decomposed by a type of bacteria that depletes the oxygen that is dissolved in the water; without this dissolved oxygen, fish and other aquatic organisms cannot survive. The Chesapeake Bay Program reported recently that areas with low (hypoxic) or no (anoxic) oxygen conditions were more prevalent in the summer of 2005 than at any time in the last 21 years since monitoring began. Images such as this one are used to track the extent and growth rate of algal blooms specifically and water quality in general.