The 600 MW Pergau Hydroelectric Project in northern peninsular Malaysia operates at a load factor of 25%. The peak station discharge is equivalent to the 1-in-2-year return period flood flow in the river. A 1.5 x 10(6) m(3) reregulating storage pond was designed to accept peak generation flows and release them into the river in a controlled manner. Karstic conditions were detected beneath the storage pond area by site investigation drilling and a microgravity survey, A risk management study resulted in the adoption of a fully lined pond with additional design measures to mitigate the geotechnical risks associated with the site. An innovative form of adjustable air-regulated siphon was developed to protect the pond embankments from being overtopped. Reregulated outflows are discharged from the pond via an outlet structure commanded by two radial gates operating on signals from the project＇s distributed control system, An operating algorithm was developed to achieve the required reregulated outflow characteristics.