WAUKESHA, Wis. (AP) — A Milwaukee suburb has finally started to pull millions of gallons of water per day from Lake Michigan after spending years seeking approval from regulators.

The city of Waukesha began the diversion Monday. City officials say 90% of the city will be using Lake Michigan’s water within five days.

The city plans to pull up to 8.2 million gallons (about 31 million liters) from the lake daily to serve as its public water supply. The city plans to return treated wastewater to the lake via the Root River, resulting in what the Wisconsin Department of Natural Resources says will be a minimal net water loss.

The city asked regulators in 2010 for permission to withdraw the water because its groundwater wells are contaminated with radium, a naturally occurring radioactive metal.

A compact between the Great Lakes states and Canadian provinces Quebec and Ontario generally prohibits diversions of water outside the Great Lakes basin but makes exceptions for communities in counties that straddle the basin’s boundaries. Waukesha County fits that exception.

Only the states were given legal authority to consider requests for U.S. water diversions. They approved the city of Waukesha’s request in 2016. The Wisconsin DNR issued final approval for the diversion in 2021.