Last Thursday started out like any other day on the Detroit River for three scientists with the U.S. Fish and Wildlife Conservation Office in Alpena, Mich. They were setting up fishing lines as part of their annual survey of the lake sturgeon population. Before arriving to check on the fourth line, scientist Paige Wigren says, the biggest thing hauled in was a 5-gallon plastic bucket.

Then everything changed.

"All of the sudden, this gray and white shadow came to the surface, and for about 5 to 8 minutes we struggled to try to get the fish into the net," Wigren recalls. She adds that when the crew all worked together, they were finally able to get the fish onto the deck of the boat. "That's when it really sunk in how large this fish was," she says.

The river monster wasn't just large, it was a record-setting giant weighing in at 240 pounds and measuring nearly 7 feet long with a girth of nearly 4 feet. Scientists believe the fish is a female and at least 100 years old.

After taking a photo of the fish lying next to one of the crew members for scale, scientists tagged the sturgeon with a microchip and released it back into the river.

In the 19th century it's estimated there were more than half a million sturgeon swimming in the Detroit River. Scientists now believe there are fewer than 7,000. The decline is largely due to overfishing and habitat destruction. But Jason Fischer, one of the other scientists on the boat, says the Detroit River's water has vastly improved in recent decades.

"We see ... world class fisheries in the Detroit River and St. Clair River," Fischer says. "I can ... think of a whole bunch of walleye fishermen who would agree with me."

Jennifer Johnson, that scientist lying next to the giant sturgeon in a photo that's gone viral, says she thinks the big catch has captured so many people's imaginations because of what it shows us about real-life magic.

"The fact that the sturgeon has survived for so long and probably has seen way more than any of us could imagine is kind of phenomenal, and just, I think everybody loves a good ... fish story," Johnson says with a laugh.

It's certainly a big fish story, which in this case involves a nearly 7-foot-long, century-old sturgeon swimming in a river that feeds industry in one of America's largest cities.

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