The fiscal year of a reclamation district shall coincide with the calendar year. The board of directors, at the close of each year's business, shall cause an audit of the books, records and financial affairs of the district to be made by a certified public accountant or firm of such accountants, who shall be selected by the district, subject to the approval of the Auditor of Public Accounts. The audit shall be in a form prescribed by the auditor, and shall contain and show the items set forth in section 46-586. When the audit has been examined and approved by the auditor, written copies thereof shall be placed and kept on file at the principal place of business of the district, and shall be filed with the Auditor of Public Accounts within one hundred and twenty days after December 31 of each year.