Wasserschloss Erlach, Water castle in Ochsenfurt, Germany.

Wasserschloss Erlach is a medieval castle in the centre of Erlach, now part of Ochsenfurt. It has an octagonal ground plan, with two-storey buildings enclosing a courtyard and a rectangular keep of bossed masonry rising 32 m above the complex. It is one of the few Staufer castles built on an octagonal plan; the moat that once surrounded it is now dry.

The Lords of Erlach built the castle in the 12th century; it was first mentioned in 1151. A new building replaced the original in the 14th century, but the German Peasants' War destroyed it in 1525, and it was rebuilt only after 1545. The Lords of Seinsheim ruled for about 200 years, followed by the Counts of Schwarzenberg for about 150; the property was then sold to the Catholic Church for one taler. In the early 19th century it was expanded to house a school and teacher's residence.

The castle's name comes from the Lords of Erlach, who built it in the 12th century; the moat that once ringed the octagonal complex is now dry. Ownership passed to the Lords of Seinsheim for about 200 years, then to the Counts of Schwarzenberg for roughly 150, before the estate was sold to the Catholic Church for a symbolic one taler.

The castle stands in the middle of Erlach, a district of Ochsenfurt; the moat that once ringed it is now drained, so the octagonal outline can be traced on foot. The 32-metre keep rises above the two-storey buildings around the courtyard. The complex is a protected monument, so visitors view the courtyard and exterior rather than the interiors.

The keep is built of bossed masonry (Buckelquader), and the whole complex is one of the few Staufer castles laid out on an octagonal plan. The moat that once ringed it is now dry.