Großer Brombachsee, Artificial lake in Franconian Lake District, Germany.

Großer Brombachsee is an artificial lake in the Franconian Lake District that stretches across three municipalities in Bavaria. At its deepest points, the water reaches approximately 100 feet (30 meters) and sits at an elevation of around 1345 feet (410 meters) above sea level.

The reservoir was inaugurated in 2000, making it the largest reservoir in the Franconian Lake District and the largest still water in Franconia. It was built to protect the Altmühl valley from flooding and to regulate water in rain-poor northern Bavaria. Water is transferred from the Altmühl via the Altmühlsee across the continental divide, filling the lake to 410.5 m; up to 403.5 m it can release water into the Regnitz, which flows to the Main.

Local sailing schools and boat rental stations line the shore, drawing families and sports groups on warm days. Many residents use the waterfront paths for cycling or spend afternoons at the swimming spots.

The 1.7-kilometre earth dam carries a walking and cycling path along its crest, with the Brombachsee power station at the operating outlet on its air side. The water sports centre of the University of Erlangen-Nürnberg, opened in July 2003, sits at the southern end of the dam. Swimming, sailing, windsurfing and kitesurfing are practised on the lake, and the DLRG and Red Cross water watch patrol it.

In June 2025, anglers caught a 2-metre, 90-kilogramme wels catfish in the lake; it was thought to have injured at least five bathers while defending a nearby nest with young. The reservoir's water level can drop noticeably in summer when no new water is fed in from the upstream lakes.