Mich. Comp. Laws § 280.496

Sec. 496. The drainage board may direct the treasurer of any drainage district to invest any surplus funds belonging to and under the control of the drainage board, in bonds and other direct obligations of the United States or in certificates of deposit or depository receipts of any bank which is a member of the federal deposit insurance corporation in such amounts and issues as shall be directed by the drainage board. The interest earnings from such investments shall be credited by the county treasurer to such drainage district funds.