<P> The northern parts of Alberta, Manitoba and British Columbia, most of Northwest Territories and Nunavut, and parts of Yukon are drained by the Arctic watershed . This watershed has been little used for hydroelectricity, with the exception of the Mackenzie River, the longest river in Canada . The Peace, Athabasca and Liard Rivers, as well as Great Bear Lake and Great Slave Lake (respectively the largest and second largest lakes wholly enclosed by Canada) are significant elements of the Arctic watershed . Each of these elements eventually merges with the Mackenzie, thereby draining the vast majority of the Arctic watershed . </P> <P> The southernmost part of Alberta drains into the Gulf of Mexico through the Milk River and its tributaries . The Milk River originates in the Rocky Mountains of Montana, then flows into Alberta, then returns into the United States, where it is drained by the Missouri River . A small area of southwestern Saskatchewan is drained by Battle Creek, which empties into the Milk River . </P> <P> Canada has produced a Biodiversity Action Plan in response to the 1992 international accord; the plan addresses conservation of endangered species and certain habitats . The main biomes of Canada are: </P> <Ul> <Li> Tundra </Li> <Li> Boreal forest </Li> <Li> Mixed forest </Li> <Li> Broadleaf forest </Li> <Li> Prairies </Li> <Li> Rocky Mountains, vegetation includes various types of tundra and forests . </Li> <Li> Temperate coniferous forests, of which the Temperate rain forests of coastal British Columbia is an example . </Li> </Ul>

What is the approximate distance of canada at its widest point