At the beginning of 2024, state archaeologists in Baden-Württemberg, southwest Germany, had an ambitious idea: to record and document all of the sunken wrecks in Lake Constance. The alpine lake once beloved of Romantic poets rests at the borders of Germany, Switzerland, and Austria and spans 207 square miles, roughly the area of a mid-sized American city.

Eighteen months on and with three-quarters of the initial phase of the project completed, the state’s office for monument preservation has announced the identification of 31 shipwrecks. They encompass a wide range of vessels and speak to Lake Constantine’s long history as a regional nexus for trade, travel, and leisure.

The sediment-covered deck of a fully preserved wooden cargo sailing ship on the bottom of Lake Constance. Photo: LAD/Marcel Edel.

Most remarkable was the identification of a fully preserved cargo ship. Although the depth and growth of mussels across its surface have obscured the full picture, researchers have called the one that has so far emerged “a rarity in underwater archaeology.” Its mast and sail supporting timber, known as a yardarm, are still present, so too are clamps on the bow designed to distribute stress, mooring pins used to secure the ship to land, and a gear ring with its attached ratchet.

“The find offers unique insights into the sailing technology and shipbuilding of historic Lake Constance ships,” Alexandra Ulisch, a researcher on the project, said in a statement. “It represents an important reference object for research.”

An underwater submersible robot is launched from the project’s MS Kormoran. Photo: LAD/Julia Goldhammer.

The first phase involved analyzing topographical maps of the lake, which in places reaches depths of 800 feet, that had previously been collected by Baden-Württemberg’s environmental agency. These maps chart elevation differences on the lake floor which researchers trawled through and identified 250 potential anomalies, areas where sudden changes in elevation seemed unusual.

Researchers have now worked through 186 of these anomalies, often using side-scan sonar, a technology that sends acoustic pulses down to the lake floor to create photorealistic images by analyzing the returning echoes. More than 80 percent of these unusual shapes were natural structures, such as the buildup of sediment or vegetation, or manmade waste, such as fishing nets. The remainder were shipwrecks that were then visited and documented either by divers or submersible robotic vehicles.

A damaged wooden barrel with a lid deep in Lake Constance. Photo: LAD/Alexander Heidacher.

“The results demonstrate the relevance of the methodological approach,” project lead Julia Goldhammer said. “Only through the combination of high-resolution data acquisition and targeted follow-up sonar investigations can natural structures be reliably distinguished from technical objects.”

Though still unfinished, the project has underscored the importance of documenting the location and condition of Lake Constance’s cultural assets, many of which were previously unknown. In one case, researchers identified a field of debris made up of at least 17 wooden barrels, many of which were extremely well-preserved. Though the ship on which the barrels were transported has not yet been identified, the project is planning follow-up investigations.

Bow of the hull of the SD Friedrichshafen II at the bottom of Lake Constance. Photo: courtesy LAD/Marcel Edel.

Another highlight was the hulls of two large metal ships that were documented using submersible robotic vehicles. They are believed to be the SD Baden and the SD Friedrichshafen II, both paddle steamers. The former was the first saloon steamer to operate on Lake Constance that ran a line between Constance and Bregenz in Austria until it was decommissioned in 1930. The latter, named for a shipbuilding town on the lake, was commissioned in 1909 and was sunk during World War II. Its sister ship, the Hohentwiel, still sails on the lake today.

“Wrecks are far more than just lost vessels,” Ulisch said. “They are true time capsules that preserve the stories and craftsmanship of days long gone.”