Whenever two counties of this state, acting under a contract made pursuant to RCW
86.13.010 through
86.13.090, shall make an improvement in connection with the course, channel, or flow of a river, shall acquire property by statute, purchase, gift, or otherwise, said counties, acting through their boards of county commissioners jointly shall have the power, and are hereby authorized to sell, transfer, trade, lease, or otherwise dispose of said property by public or private, negotiation or sale. The deeds to the property so granted, transferred, leased, or sold shall be executed by the chair of the meeting of the joint boards of county commissioners, and attested by the secretary of said joint meeting where the sale is authorized. The proceeds of the sale of said property shall be used by said counties for the carrying on, completion or maintenance of said improvement, as directed by the boards of county commissioners of said counties acting jointly.