In cases where the United States has constructed irrigation works, canals and laterals under the provision of the Act of Congress of June 17, 1902, known as the reclamation act, or acts amendatory and supplementary thereto, within the boundaries of an irrigation district, or for the irrigation of lands within an irrigation district organized either before or after the construction of said works, the board of directors of said irrigation district may enter into a contract with the United States to care for, operate and maintain the said works, or parts thereof, and may levy assessments for the purpose of such operation and maintenance of said works, and collect the same in the same manner as in this chapter provided.