Scientists have fanned out across the Great Lakes' frozen surfaces to learn what happens underwater during winter.
U.S. and Canadian teams have visited all five lakes in recent weeks.
They've drilled into the ice to take samples and gather data. Researchers have long done such field work at other times of year, assuming not much is happening in the lakes during winter.
But they recently concluded that there's more activity than they realized.
They say it's urgent to get more information now, as climate change reduces the Great Lakes' ice cover.
One crew from Central Michigan University focused on Lake Huron's Saginaw Bay, a favorite of anglers seeking perch and walleye.
