The focal point of the Putrajaya is the development of a 400 hectares lake by construction of the Putrajaya Main Dam across Sg. Chuah. The Putrajaya Main Dam is an earthcore rockfilled dam, about 35m high and 800m long. A large part of the dam foundation area consists of soft alluvial deposit, which posed a risk to the stability and the long term settlement of the dam. A Labyrinth spillway with a crest length of 290m was designed to pass the designed flood of 1187 m 3 /s and to limit the flood rise to below 2.0m which is critical to the operation of the lake. The Labyrinth spillway is a first of its kind in Malaysia. A hydraulic model was carried out to confirm the spillway design parameters.