<P> The Elizabeth River estuary is important for Norfolk, Virginia, Chesapeake, Virginia, Virginia Beach, Virginia and Portsmouth, Virginia . It has been polluted by nitrogen and phosphorus, but also toxic deposits from the shipbuilding industry, the military, the world largest coal export facility, refineries, loading docks, container - repair facilities and others, so fish had been "offlimits since the 1920 _́ s". In 1993, a group formed to clean it up, adopting the mummichog as a mascot, and has removed thousands of tons of contaminated sediment . In 2006, a 35 - acre biological dead zone called Money Point was dredged out, and shown fish to return, the wetland to recover </P> <P> A dead zone exists in the central part of Lake Erie from east of Point Pelee to Long Point and stretches to shores in Canada and the United States . The zone has been noticed since the 1950s to 1960s, but efforts since the 1970s have been made by Canada and the US to reduce runoff pollution into the lake as means to reverse the dead zone growth . Overall the lake's oxygen level is poor with only a small area to the east of Long Point that has better levels . The biggest impact of the poor oxygen levels is to lacustrine life and fisheries industry . </P> <P> A dead zone exists in the Lower St. Lawrence River area from east the Saguenay River to east of Baie Comeau, greatest at depths over 275 metres (902 ft) and noticed since the 1930s . The main concerns for Canadian scientists is the impact of fish found in the area . </P> <P> Off the coast of Cape Perpetua, Oregon, there is also a dead zone with a 2006 reported size of 300 square miles (780 km2). This dead zone only exists during the summer, perhaps due to wind patterns . The Oregon coast has also seen hypoxic water transporting itself from the continental shelf to the coastal embayments . This has seemed to cause intensity in several areas of Oregon's climate such as upwelled water containing oxygen concentration and upwelled winds . </P>

What are the causes and effects of the dead zone in the gulf of mexico