Lurking on the bottom of Lake Minnetonka are long-forgotten relics, clues to Minnesota's past that a pair of archaeologists are seeking to explore.

On Tuesday, Chris Olson, Ann Merriman and a team of volunteers started diving in their third year of investigating and identifying dozens of wrecks that sank long ago on the Twin Cities' most popular lake. The husband-wife duo, the only underwater archaeologists in Minnesota, started the decades-long project to survey the 14,000-acre lake in 2011, but this year's dives continuing the work almost got derailed.

For the first time, the researchers were rejected for limited state Legacy funds and are now relying on private donations to keep the work afloat during their small window of time for the underwater work this summer.

"It's our shared history," said Merriman, 49, who grew up in Delano and returned to the area with her husband to launch the nonprofit Maritime Heritage Minnesota in 2005. "The underwater sites on Lake Minnetonka have been ignored for too long."

The couple launched a campaign to raise up to $10,000 in donations to back this summer's work. So far, they've raised $4,300, which will go toward investigating three wrecks and 22 so-called anomalies that could either be human-made or, as they found out Tuesday, something as insignificant as a large tree that sonar picks up underwater.

Make no mistake: The couple aren't treasure hunting: They don't raise the wrecks, and looting is illegal. Rather, they're more like history hunting, carefully identifying wrecks and spending hours poring over historical records and old newspaper clips to research the story behind each wreck.

"It's like a crime scene; it's trying to figure out what happened," said Olson, 50. "We consider this like an underwater museum. The wreck becomes the only clue to the past."

Before they started work, there were six known wrecks on Lake Minnetonka. Since then, Olson and Merriman have identified 30 more and on Tuesday, they identified their 31st — a fiberglass boat. Tracing each wreck to the original owner, builder or those involved in the sinking, either intentional or accidental, helps link the past together and provide closure, they say.

"We dive to answer questions," Merriman added. "It's such a big job."

The couple studied all of Minnetonka's lake bottom in 2011 and 2012 with sonar equipment. Then, in the past three years, they've been identifying up close and researching the wrecks on the Twin Cities' busiest lake. They've found everything from sunken motorboats and cabin cruisers to a passenger steamboat that sunk in 1899, a 1936 Plymouth Sedan, a 1974 Caprice Classic Coupe and an oak wood model barge from 1879 — the oldest wreck still on the bottom of the lake and one of three of its kind left in the country.

"They're doing what they love and really informing Minnesota," state archaeologist Scott Anfinson said, adding that their sonar work is the first systematic look at the lake's bottom. "Minnesota is getting a real benefit."

The couple have also done work on Lake Waconia and White Bear Lake, but have found more wrecks in the waters of Minnetonka — which has a legendary history of boating and sailing. The muddy ground of the freshwater lake, which mostly is 30 feet deep but sinks as deep as 113 feet, also has helped preserve many of the wooden structures.

"They're so passionate about it and so ethical," said Mark Slick, a volunteer who helps the couple on dives. "These guys are all about preservation and history."

The 19 Legacy grants they received in the past five years provided nearly all their funding, so when they didn't get it this year, they had to turn to private donations for the first time. The St. Paul couple get by with little — "we almost work for free," Merriman said, adding they don't even own a boat — and will reapply for a Legacy grant in July for the end of the year.

After all, the work is far from over. Merriman said there are more than 700 anomalies they still need to dive to investigate and research on Lake Minnetonka.

"There are so many questions we have," she said. "This is a lifetime of work we have here."

Kelly Smith • 612-673-4141

Twitter: @kellystrib