The pact, reached after four years of talks, also seeks to encourage conservation of water by the states and Canadian provinces around the Great Lakes. It allows lake water to be transferred only to communities within the Great Lakes and St. Lawrence River Basin.

"The lakes represent a fresh water ecosystem that's unique on our planet, supporting thousands of species, including human beings. These agreements will protect our Great Lakes from the threats of diversions outside this basin," said Wisconsin Gov. Jim Doyle, the incoming chairman of the Council of Great Lakes Governors.

The pact was motivated largely by fears that states in the booming but arid Southwest will try tapping into the lakes, which hold 90 percent of the nation's fresh surface water, as their populations and political clout grow.

Molly Flanagan, Great Lakes water resources advocate for the National Wildlife Federation, said available fresh water will become the "new oil" as more states and countries begin looking for the resource.

"Look at statistics from the United Nations and you'll see clean water is increasingly scarce throughout the world," Flanagan said.

The agreement requires the approval of legislatures in all eight states before Congress could consider making it law.