RCW 86.12.010

The county commissioners of any county may annually levy a tax, beginning with the year 1907, in such amount as, in their judgment they may deem necessary or advisable, but not to exceed twenty-five cents per thousand dollars of assessed value upon all taxable property in such county, for the purpose of creating a fund to be known as "river improvement fund." There is hereby created in each such river improvement fund an account to be known as the "flood control maintenance account."