On January 1 of each year the Secretary shall report to the Congress, beginning with the fiscal year ending June 30, 1969, upon the status of the revenues from and the cost of constructing, operating, and maintaining each lower basin unit of the project for the preceding fiscal year. The report of the Secretary shall be prepared to reflect accurately the Federal investment allocated at that time to power, to irrigation, and to other purposes, the progress of return and repayment thereon, and the estimated rate of progress, year by year, in accomplishing full repayment.