Lake Champlain has unusual characteristics. It occupies a long, deep, and narrow valley; it has a northerly flow; and for a period after the glaciation the lake was marine. It then became the sixth largest lake in the United States. Lake Champlain may have the largest shore development index of any lake in the United States.

The lake occupies a north-south fault zone, and extends 174 km from Whitehall, N. Y. to its outlet in Canada. The lake flows northerly through its outlet, the Richeleau River, into the St. Lawrence River near Montreal. The maximum width of the lake is 19 km. The drainage basin of the lake of 19,881 km2 includes portions of the States of New York and Vermont and the Province of Quebec in Canada.

The basin was overridden by the Wisconsin glaciation during the Pleistocene. As the ice melted towards the north, proglacial Lake Vermont was formed and flowed south through the Hudson valley. When the ice margin retreated north of the St. Lawrence Valley, the Champlain basin was inundated with saline ocean water, forming the Champlain Sea. After glacial rebound of the land to the north, the marine incursion ended and the present Lake Champlain was formed about 12,000 years B. P. The uplift resulted in a complex and irregular lake basin with drowned valleys to the east and precipitous cliffs to the west. Large islands to the north, more than 70 islands in the lake, and peninsulae have divided the lake into five major basins. The southern lake is riverine and opens into the main basin. The Missisquoi River delta forms Missisquoi Bay to the northeast. The large islands to the north and natural causeways form Malletts Bay. Between these two bays, and to the east of the islands is the Northeast arm of the lake. Each of these five basins exhibits distinct limnological characteristics.

Lake Champlain has been the focal point for much of the early history of this part of North America. For nearly 150 years after being discovered by Samuel de Champlain in 1609, the lake was the focus of the British, French, and Indian wars; the lake was the scene of significant naval battles during the Revolutionary War and the war of 1812.

Approximately 9.830 km3 of water drain from 19,881 km2 of land into the lake per year providing a refilling rate of 2.6 years at average lake level. The population in the basin is approximately 500,000. Although the lake appears to have been deteriorating since the turn of the century, the trend for inter- governmental cooperation is increasing. Environmental sense is strong among the inhabitants (Q).