Home to the Southern Watershed, located in southeastern Virginia and making up the southern portions of the cities of Chesapeake and Virginia Beach, this is one of the most biologically diverse regions of the state. This area supports more than 40 rare plant species and 10 terrestrial, estuarine, and palustrine wetland communities. Within these ecosystems, the fishing industry prevails and the economic value of the annual commercial fishing harvest is about $500 million. But the mix of the catch is changing and several valuable commercial aquatic species of the Bay have declined over the years. What is the MOST LIKELY reason for this decline in aquatic species in Virginia's Southern Watershed?