The House approved a bill Tuesday to protect the vast body of fresh water in the Great Lakes region by prohibiting almost any diversion of it to places outside the lakes’ basin and requiring the eight states bordering the lakes to follow new conservation standards.

The vote was 390 to 25 in favor of the bill, which has already been passed by the Senate and is expected to be signed by President Bush.

The measure, the Great Lakes Compact, was negotiated by the eight states. A decade in the making, it is intended to ease longstanding fears that states outside the region, or even other countries, could tap into the lakes, possibly deplete them and do long-term damage to their basin’s natural environment and economy.

Together, the five Great Lakes account for 20 percent of the world’s supply of fresh surface water, and an estimated 40 million people get their water from the lakes’ basin. Scientists and environmental advocates who backed the legislation said they considered the lakes not a regional resource but a national one, whose health and integrity, they said, are in the entire country’s interest.