Whatever you do, don’t call them treasure hunters.

It’s true that underwater archaeologists Ann Merriman and Christopher Olson hunt for historical treasures while exploring the bottoms of Minnesota lakes. “But we don’t romanticize it,” Merriman said.

Merriman and Olson, a St. Paul married couple who founded and operate Maritime Heritage Minnesota (MHM), this year located 10 previously unrecorded sunken boats in Lake Minnetonka, some more than 100 years old. Also three snowmobiles, two trees, two big rocks and a barrel.

Merriman and Olson are the only two licensed underwater archaeologists in Minnesota, combing lakes for sunken artifacts, primarily boats. They basically do the same work archaeologists do on dry land, except instead of digging in dirt they dive into water and sweep away silt.

The couple spend summers using sonar equipment and diving to inspect wreckages, aided by volunteers and sponsored by grants from the state’s Legacy Amendment. Their winters are devoted to researching the boats and wrecks they find in old newspapers and other databases.

“Boats, no matter what their age, are windows into the past,” Olson said. “Historical documents don’t always survive. What’s left are boats.”

Minnesota’s cold freshwater lakes effectively preserve underwater wreckages, telling stories about the lives of previous generations in a state whose waters shaped history.

“We do archaeology to answer questions,” Merriman said. “Why did they build this boat this way? What were the conditions? Were they fishing or gathering wild rice, looking for clams or taking their best girl out on a Saturday?”

They have investigated lakes across the metro area. But Lake Minnetonka, with its history of logging, commerce and hotels, is particularly rich in vestiges of the past.

Like a crime scene

Before paved roads were build around Lake Minnetonka, the lake itself offered the most efficient way to transport people and goods such as lumber and mail. Donaldson’s, the now-defunct Minneapolis department store founded in the late 19th century, used to deliver items by boat. Boats designed to look like trolleys carried people between Excelsior, Wayzata and other lakeside cities.

American Indians used the lake long before white settlers arrived. One of the oldest boats discovered (not by Merriman and Olson), an 11th-century dugout canoe, came from Lake Minnetonka. “For a long time, boats were the most technologically complex things humans made,” Olson said.

Many of the wrecks MHM studies are more recent, but they consider those compelling, too.

A few years ago, the couple traced a sunken boat near Spring Park to a 1952 accident. Online records showed that a 14-year-old boy had survived. They contacted someone with that name and, sure enough, it was the boy — now a man in his 70s.

Merriman and Olson stress, frequently and vehemently, that they don’t remove artifacts from lakes. Removing anything from a Minnesota lake is illegal, unless it belongs to you and was lost recently. Dredging up so much as an old anchor to display on a mantel is considered looting.

The couple didn’t approve of the 1980 dredging of the steamboat Minnehaha, a 1906 passenger transit boat that was restored and brought back as an excursion boat in 1996.

“People get mad when we say it shouldn’t have been raised,” Merriman said. But they’re firm about leaving artifacts undisturbed. When they come upon a sunken boat, they remove only tiny samples of wood, metal, fiberglass and other materials needed to research the vessel’s history.

“We treat a wreck scene as if it were a crime scene,” Olson said.

Once when Olson was inspecting a boat wreck underwater, a metal plate engraved with the name of the boat’s manufacturer broke off in his hands. They took the plate home, cleaned it and identified the boat as a craft built in 1960 that sunk, they believe, in a 1965 tornado. They then treated the metal to preserve it, put it in a Ziploc bag, dove back down to the wreck and screwed it to the boat’s deck.

So in the unlikely event that Merriman and Olson ever come upon a chest of doubloons, they won’t strike it rich. They’ll leave the gold coins just the way they found them (and will keep the location classified, as they do with all their finds).

“We’re not looters,” Merriman said. Though she said they would be eager to investigate the era and circumstances under which the coins were left.

“That’s what would interest us,” she said, “the history of the gold.”