After the completion of a flood control project or a portion thereof and, in the case of projects constructed by the federal government, after such project or a useful portion thereof has been turned over to the state by the federal government, such projects may be operated and maintained by the Water Resources Commission for the primary purpose of flood control; or, when the commission deems such action to be in the public interest, the commission may enter into agreements with public or quasi-public bodies and other persons to operate and maintain such projects. [1957 c.466 § 6]