Except when the purpose of the permitted draw down is to remove or eliminate the impoundment, the permittee shall refill the impoundment when the permit expires or the work is completed, whichever occurs first. In refilling the impoundment, the permittee is responsible to allow a minimum flow of water determined by the Commission to be sufficient at all times to flow in a natural stream on which the impoundment is located to provide for the protection and conservation of fish downstream from the site.
58 Pa. Code § 51.87