TRAVERSE CITY, Mich. - A U.S. government analysis says the Great Lakes region could see water shortages in some areas because of climate shifts or increased demand.

The five-year study by the U.S. Geological Survey was obtained by The Associated Press ahead of its scheduled release today.

The report says the Great Lakes hold six quadrillion gallons of water -- enough to spread a foot-deep layer across North America, South America and Africa.

Just one per cent of the lakes' water is replenished annually through runoff and precipitation, and vast amounts are removed for agriculture, industry, drinking and other uses.

But the report says the overall supply is so big that withdrawals have had little effect on the Great Lakes system.

But weather and climate have significant effects on groundwater and lake levels and stream flow rates.

Declining lake levels over much of the past decade resulted largely from drought and warming temperatures that limited winter ice cover and boosted evaporation.