Großer Alpsee, lake in Immenstadt, Bavaria, Germany

The Großer Alpsee is a large natural lake in Immenstadt im Allgäu, surrounded by meadows, forests and gentle hills. The water is characterized by shallow shores covered with sand and gravel, making it accessible for various activities throughout the year.

The lake is owned by the Free State of Bavaria and managed by the Bavarian Administration of State Palaces, Gardens and Lakes. Since 1983 the Allgäu Triathlon has been held in it, with one world championship, two European championships and eleven German championships staged as part of the event. Since 2003 the one-hour round trips have been run with a Lädine, the Santa Maria Loreto.

Since 2003, one-hour cruises have been offered in summer on a Lädine, the Santa Maria Loreto, a replica of a historic Lake Constance sailing cargo boat. The Segelclub Alpsee-Immenstadt holds several regattas a year in different boat classes, and since 1983 the Allgäu Triathlon has been staged in the lake, with one world championship, two European championships and eleven German championships held within it.

The lake lies west of Immenstadt in the Konstanzer Tal, with the Buchloe–Lindau railway running close along the north shore. Swimming spots are at the south-west, south-east and east shores, where a campsite also stands. Winds in the eastern part often swirl and can shift direction quickly, so sailors should watch the water. Since 2003 one-hour round trips have been offered on the Lädine Santa Maria Loreto.

The Allgäu Triathlon has been held in the Großer Alpsee since 1983, making it one of Germany's longest-running triathlon events; it has hosted one world championship, two European championships and eleven German championships. On 1 March 2026 Paul Bieber set a world record here in the ice triathlon, swimming 250 m in 4.4 °C water, cycling 12.5 km and running 2.5 km from Bühl am Alpsee to Oberstaufen in 50:49 minutes, all in a single tri-suit.