Twenty miles south of Duluth, the St. Louis River cascades down the face of the Fond du Lac hydroelectric dam.
Two men in waders step carefully toward the middle of a big pool in the river. Walking on boulders set there two years ago to make a more welcoming place for sturgeon, they look for the big fish.
State Department of Natural Resources managers hope that for the first time in decades, the sturgeon will be able to reproduce in the stream. When they see one, they use a long-handled net to scoop it up.
On shore, they lay it on a board outfitted with a tape measure. The fish are pretty calm, but they're so big and strong it takes two men to hold them down.
The fish is 101.2 centimeters long -- about three feet -- and 13.5 pounds.
Nick Frohnauer, a DNR assistant area fisheries manager, and two colleagues use an electronic sensor to check for identifying tags placed under the skin. There's no tag on this one, but they can tell he's a male.
"You get a little bit of milt that comes out if you give him a gentle squeeze," Frohnauer said. "So this little guy's ready to do his thing."
"Milt" is the fish version of sperm. Now they're cutting off a thin slice of fin. That'll tell how old he is.
The fish, which look like small aquatic dinosaurs, are dark, almost black. They don't have bones, and they don't have scales. Just under their smooth skin are five rows of something called "scutes."
"Like little plates of armor," Frohnauer said. "The ones on the top often have a little bit of a hook to them, they're real sharp. They are prehistoric fish."
They haven't changed much in 200 million years.
On the underside, a sturgeon has four big whiskers that help it find food. Their prey -- mussels and other bottom dwellers -- don't have much of a chance, no match for the sturgeons' huge, flexible mouths.
"A sturgeon actually protrudes its mouth like a hand and grabs its prey with its lips like they're fingers and pulls the prey back into their mouth," said John Lindgren, a DNR manager in the Duluth area.
Lindgren is glad to see so many fish, but what he really wants to see is eggs.
"It has been 27 years since we began our stocking, so you'd assume that we have females old enough to spawn here, and we have seen larger fish," he said. "We just haven't documented that they've been successful in reproducing yet."
Sturgeon don't mature for 18 to 25 years. The DNR started stocking the St. Louis River 27 years ago. The babies they put in then are now just barely old enough to reproduce.
Fisheries managers improved the area just in time. They spent $150,000 to rearrange the stream bed. They created lots of the kinds of places where sturgeon like to lay eggs: above the rock wall where the current slows a little, in small room-like structures surrounded by rocks and in the eddies formed by boulders.
The designer is Luther Aadland, a DNR river ecologist. In a wetsuit and goggles, he's been dipping in the water to see if he can see any sticky, BB-sized eggs. So far, no luck; in fact, Aadland said the sturgeon don't seem to be feeling particularly amorous.
"When they get going, it's quite a sight," Aadland said. "Water's flying. It'll actually shake the boulders when they get going."
All that must be for another day. These men are operating on a long-term vision. Lindgren said someday people could fish for sturgeon and eat them. But he wants to see another generation of sturgeon first.
"If there's an egg laid here and we produce fish from 2010, I'd like to see those fish come back in 20 years," he said.
That would mean the population was surviving on its own.
These are fish that would thrill anglers. The biggest one on this day gives the researchers some good exercise. It's more than four and a half feet long and as big around as a small watermelon.
"Chances are that one's going to put some eggs on the ground," Lindgren said.
There's a sense of satisfaction, and hope, as they slide a mature female nearly 50 pounds in weight back into the water.
"That's the biggest one by far," Frohnauer said. "Look at the girth on that fish. There she goes."
Over the summer, DNR workers will keep looking for those eggs, and for any sign that their decades-long work is finally producing a self-sustaining population of sturgeon.