Wandsbeker Seeschwimmen Ostende

A groundwater spring bubbling up inside an abandoned clay pit gave Hamburg's eastern suburbs one of their most characterful open-water bathing lakes. This hidden pond sets the stage for the Wandsbeker Seeschwimmen Ostende, an open water swimming race held in the sheltered waters of Freibad Ostende in Hamburg-Tonndorf. Organized by the Hamburger Schwimmverband, the competition gathers swimmers each September to close out the northern German summer in calm, spring-fed freshwater. The race unfolds over a compact 250-metre loop clearly marked by buoys across the lido. At the heart of the day's schedule is the 1,000-metre Jedermann event, where swimmers tackle four full laps of the circuit. You do not need a club licence or federation membership to line up for this main distance, making it an accessible gathering for local lake enthusiasts, masters, and independent open-water travellers alike.

Three distinct age brackets cover everyone from teenagers aged twelve to veteran masters up to ninety-nine years old. Swimmers take to the water in an energetic mass start, either plunging directly from the bath's wooden jetty or stepping in to start from the surface of the lake. Behind the jetty, a broad expanse of open water allows the pack to spread out comfortably before jostling for position around the turn buoys. Swimmers settle into their stroke, feeling the crisp bite of the lake beneath the low autumn light. Because the event takes place in late September, clear thermal rules protect everyone on the course. Starts are only released if the lake registers at least 16 degrees Celsius, preventing dangerously cold immersion.

Swimmers can pull on their neoprene suits for buoyancy and warmth whenever the water stays below 24 degrees Celsius. Out on the circuit, safety personnel patrol the perimeter on rescue boards and as dedicated rescue swimmers. In the 1,000-metre race, a 40-minute cutoff behind the leading swimmer ensures all participants return safely. Alongside the distance swim, local clubs battle through a brisk 4 x 107-metre relay that adds a burst of sprinting excitement to the shoreline.

Ostender Teich: the spring-fed clay pit lido

Ostender Teich was never a natural geological depression: it owes its existence to an old industrial clay pit. An association was established in 1986 to manage the open-air bath at Ostende. Today, leafy allotment gardens encircle the quiet banks of the pond, creating a green buffer hidden deep inside Tonndorf. Only about ten percent of the water's surface is enclosed as the public summer bath. Yet the natural bathing beach at the northeastern corner is cherished well beyond the borders of Tonndorf. On ordinary summer afternoons, the waterfront buzzes with community life. Daring swimmers climb the three-metre diving platform to launch themselves into the deep water, while small children splash safely in an enclosed non-swimmer basin.

The Wandse and Rahlau streams around Tonndorf

Directly outside the boundary fences of Freibad Ostende, the Wandse stream curves along the northern and western perimeter of the lake. Rising far to the northeast near Siek in the Stormarn district of Schleswig-Holstein, this historic watercourse once powered dozens of water mills along its winding route toward Hamburg. Another historic urban waterway converges with the system. The Rahlau stream marks the boundary between the districts of Jenfeld and Tonndorf before emptying directly into the Wandse. Artists, conservationists, and the NABU created an effective natural fish pass that allows aquatic life to navigate around the dams of the Wandse. The Wandse flows through Eichtal Park. Downstream of the Mühlenteich millpond, the river transforms into the Eilbek and then the canalised Eilbekkanal. It finally reaches the expansive waters of the Außenalster.

Ahrensburg Tunnel Valley: glacial waters near Tonndorf

The broader hydrology of this corner of Hamburg has roots in deep glacial history. About four kilometres from Ostender Teich, glacial meltwater carved the Ahrensburg Tunnel Valley. In a curious post-glacial twist, the Stellmoorer Quellfluss stream running through the valley now flows in the exact opposite direction of the ancient glacial meltwater that carved the land. During the 1930s, agricultural projects straightened and deepened the stream, but between 1978 and 1982 it was designated as a protected nature reserve. These secluded brooks are home to native fauna. Among them is the brook lamprey, an ancient, jawless creature whose presence might sound intimidating until you realize adults are tiny, measuring only twelve to fourteen centimetres in length and posing no harm whatsoever to humans.

Sharing the same clear gravel and sand beds is the gudgeon, a gentle bottom-dweller reaching barely nine to thirteen centimetres. These small fish spend their days quietly sifting through the silt for insects, larvae, and worms, completely indifferent to passing swimmers.