“That’s something like $26,000 worth of extra ore per inch, so if you multiply that by 2 or 3 inches of water level, and then multiply it by more than 30 trips over the course of a shipping season, it adds up to some significant benefits,” Hron said.

Quick turnaround

Great Lakes water levels began quickly dropping in the late 1990s, and that downward trend lasted 15 years. Warm lake temperatures led to high evaporation rates, causing the decreased levels, said Drew Gronewold, a University of Michigan environmental science professor and former hydrologist at the National Oceanic and Atmospheric Administration’s Great Lakes Environmental Research Laboratory.

“There really isn’t a period of below-average water levels in the record for quite that long a time period,” Gronewold said. Great Lakes water data goes back a century.

Gronewold said the quick transition was “one of the most rapid water level increases in history.”

Rain, snowfall

Lauren Fry, a hydrologist with the U.S. Army Corps of Engineers’ Detroit district, said the current spike in water levels was driven by an increase in rain and snowfall over the Great Lakes and the surrounding land that runs off into them.