An estuary is an area where freshwater and salt water mix together to form a region of very high nutrient levels and productivity. The world's largest estuary is the Gulf of Saint Lawrence river (which connects the Great Lakes to the Atlantic Ocean). A major portion of this estuary is in Canada, and the river has a length of over 1,900 square miles. The watershed of the estuary spans over 390,000 square miles. 5 out of 10 provinces of Canada border this Gulf and a number of streams contribute to the water of the river. In comparison, the largest estuary of United States is the Chesapeake Bay, which has a watershed of about 64,000 square miles. Estuaries have to be protected against too much human intervention, such as urbanization, overfishing, etc.
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