Iowa Code § 468.174: Membership in the national drainage association.

1. Any drainage district may join and become a member of the national drainage association. A drainage district may pay a membership fee and annual dues upon the approval of the drainage board of such district, but not in excess of the following:

a. One hundred dollars for drainage districts having indebtedness in excess of one million dollars.

b. Fifty dollars for drainage districts having an indebtedness of five hundred thousand dollars and less than one million dollars.

c. Twenty-five dollars for drainage districts having an indebtedness of two hundred fifty thousand dollars and less than five hundred thousand dollars.

d. Ten dollars for drainage districts having an indebtedness less than two hundred fifty thousand dollars.

2. The annual dues for any district shall not exceed one-twentieth of one percent of the outstanding indebtedness of the district.