Bodensee Openwater - Seequerung Meersburg / Konstanz

Before six in the morning, while the shoreline between Meersburg and Konstanz still rests in pre-dawn twilight, swimmers wade into Lake Constance for a direct crossing of the lake. The Bodensee Openwater - Seequerung Meersburg / Konstanz is an open water swimming race across the wide waters of Lake Constance, held between Meersburg and Konstanz in the state of Baden-Württemberg, Germany. Founded by the Bodensee Openwater Team, the organization has staged open-water lake crossings since 2017. Slipping into the vast freshwater expanse at dawn strips away any sense of land, leaving only the open channel between the northern and southern shores. The crossing takes place as part of a summer calendar running through July and August.

Swimmers choose between two flagship courses: a one-way crossing of 5,000 meters and a two-way round trip of 10,000 meters. Early summer conditions offer mild and inviting freshwater, shedding the sharp chill of spring while staying brisk enough to sustain high tempo across open water. In past editions, swimmers have pushed away from the bank into almost completely flat, mirror-like water, feeling an instant lift as the rising sun crested over the silhouettes of lakeside trees. Those taking on the 10,000-meter course face the unique test of the return leg, swimming directly into the low morning glare that spreads across the water. Navigating straight toward the eastern light requires steady rhythm and head-down focus, but mid-lake logistics keep swimmers well supported. In past editions, swimmers paused mid-course alongside unmanned floating refreshment tables stocked with energy bars, fresh bananas, and isotonic drinks before turning their strokes back toward the opposite bank.

Q5 and Q10: classes, rules and the Meersburg shore

The Konstanz–Meersburg swim of the Bodensee Openwater Team is scheduled for Saturday 26 June 2027 over two distances, Q5 and Q10. Swimmers in the Bodensee Openwater events must tow a swim buoy, either their own or one from the organisers, and the organisers supply the swim cap that must be worn. Wetsuits are allowed in the Bodensee Openwater events, but not when the water temperature officially measured on the morning of the event is 25 °C (77 °F) or more. Bodensee Openwater groups its swimmers into four speed classes, from about 2.5 km/h in Class I to about 4.0 km/h in Class IV. The timing at Bodensee Openwater uses transponder chips that are handed out on the day of the event and collected again after the swim. The DLRG Bodenseekreis secures the Bodensee Openwater swims with boats, stand-up paddleboards and canoes. In 2026 the Bodensee Openwater season included an anniversary swim from Konstanz to Meersburg, next to the 11 km crossing from Friedrichshafen to Romanshorn. On the Meersburg side, the lower town and the upper town are reserved for pedestrians only, and they are connected by two stairways and a steep street called the Steigstrasse. Meersburg is the northern terminus of a car ferry service to Konstanz.

The Konstanzer Trichter and the Seerhein outflow

At the southern terminus of the crossing, the lake narrows sharply where the city of Konstanz guards the western edge of the Upper Lake. Here, the open expanse funnels into the Constance Hopper, a broad natural bay lying east of Konstanz and north of Kreuzlingen. This bay gathers the immense volume of the lake and funnels it into the opening of the Seerhein, which serves as the primary river outflow for the entire Upper Lake. The Seerhein cuts straight through Konstanz beneath the arches of the Old Rhine Bridge, varying between 100 and 500 meters wide with depths plunging between 7 and 25 meters. Along its western two-kilometer stretch, this river channel forms the international boundary between Germany and Switzerland.

The Constance Hopper itself holds a unique legal status as the only portion of the Upper Lake where an exact territorial border between the two nations has been formally demarcated. Underneath the water, the riverbed is blanketed in thick lake sediments of chalk and crushed shell sand, measuring up to 13 meters deep in several sections. The natural dynamics of this basin have produced remarkable hydrological events over the centuries: on February 23, 1549, the famous 'Water Miracle of Constance' saw seiche standing waves surge through the channel, causing the local water level to rise and fall by more than half a meter every fifteen minutes.

Dominikanerinsel and the historic waterfront of Konstanz

The glacial moraines along the shore of Konstanz provided firm, stable ground for human habitation stretching back thousands of years. In the shallow water around what is now Dominikanerinsel, archaeologists uncovered Neolithic pile-dwelling settlements dating back to the fifth and third millennia BC. These prehistoric lakeside villages now enjoy international protection as a UNESCO World Heritage Site. By the Middle Ages, the strategic value of this shoreline made Konstanz an indispensable crossroads. The city controlled the only bridge across the Rhine in the entire region and reinforced its position by building fortifications directly into the lake itself, complete with a water-powered grain mill anchored to the river bridge. Dominikanerinsel was separated from the medieval town center by a six-meter-wide defensive moat. Down on the bustling modern harbour stands the Konzilgebäude, famous as the site of the only papal conclave ever conducted north of the Alps.

Wollmatinger Ried: the protected reed islands of Untersee

The Wollmatinger Ried nature reserve lies next to the island of Reichenau, an extensive wetland belt dominated by dense reed beds that rim the water. Tucked inside this protected wetland sits Langbohl, a secluded island measuring 454 meters long and up to 114 meters across. Shrouded almost entirely in tall reed beds, Langbohl is separated from neighboring banks and adjacent islands by narrow channels fed by the Seerhein. Because of its delicate marshland habitat, all human access to Langbohl is strictly forbidden, keeping it untouched as a safe haven for local wetland species. Just across a narrow channel measuring between 30 and 50 meters wide rests Triboldingerbohl, the fourth largest island in Lake Constance at over 135,000 square meters. Measuring 780 meters in length, Triboldingerbohl belongs to the Wollmatinger Ried sanctuary and borders the Ermatinger Becken.

Mainau Island: molasse cliffs and Roman naval history

To the north, where the lake branches into the Überlinger See, the landscape is shaped by the limestone bluffs of Mainau Island. Mainau rises out of the water as a massive outcrop of molasse rock, harboring archaeological evidence of six Neolithic pile dwellings that stood along its shorelines around 3000 BC. Centuries later, in 15 BC, the Roman general Tiberius recognized the strategic advantage of this rocky island and used it as the naval base for his fleet during the military campaign against the Vindelici. In 1272, the Teutonic Order took command of Mainau after receiving the territory from the ministerial Arnold von Langenstein. On the southwestern shore of the island, overlooking vineyard slopes that drop straight toward the lake, stands the Schwedenturm, a twenty-meter-high stone watchtower built in 1588.

Along the water below, the island's famous shore arboretum—planted by Grand Duke Friedrich I in 1856—shelters one of the oldest dawn redwood trees in Germany. Sighting across this historic lake surface at dawn, every stroke between Meersburg and Konstanz connects you to thousands of years of human settlement anchored in these clear alpine waters.