TRAVERSE CITY, Mich. -- The U.S. and Canada have done well at preventing Great Lakes water from being overused or raided by outsiders but should take additional steps to strengthen their legal protection against future grabs, an advisory organization said Tuesday.

A compact between the region's eight states, and similar legislation approved by the provinces of Ontario and Quebec in the past decade, banned nearly all diversions of water outside their geological boundary and set conservation requirements for users within the region. Since then, no exports have been approved that would have "significant negative impacts on the ecological integrity of the Great Lakes," said a report by the International Joint Commission, which advises both nations on issues affecting shared waterways.

"This is really a model for watersheds all over the world, emphasizing water conservation and stewardship," said Benoit Bouchard, one of Canada's representatives on the six-member commission and a former minister of industry, science and technology.

The report updated an assessment the commission made in 2000, amid concern that Sun Belt states -- or even foreign powers -- might use interstate commerce law or trade pacts to justify piping water from the Great Lakes.

Despite the legal barriers to such diversions that the region's governments have set, pressure to make exceptions or allow excessive withdrawals within the region could intensify as climate change worsens problems such as droughts and algae pollution, the report said.

It advised the governments to consider making the protections even tighter by designating the lakes as resources held in public trust for uses such as drinking, fishing and watering crops.

Adopting the public trust doctrine as a "backstop" to existing policy would bind governments to "sustain these waters unimpaired as much as possible from one generation to the next," said Jim Olson, an environmental attorney and president of For Love of Water, an advocacy group that urged the commission to endorse the legal principle.

The commission also called for better tools to measure Great Lakes water use and detect degraded groundwater supplies, and for upgrading pipes and other infrastructure to reduce waste.