ORS § 547.470
When, in the judgment of the board of supervisors of any drainage district, it is deemed necessary or expedient to drain any lake, which entails extra or additional work in excess of that required in the drainage of lands of higher elevation and where the cost of maintenance and pumping to maintain drainage of such lake will be in excess of that necessary for the reclamation and maintenance of lands within the district other than such lake, an extra assessment or charge for such additional work or a higher rate for such pumping and maintenance may be charged and made against the lands, or owners or occupants of the lands, covered by such lake, to the extent of the respective additional benefits to such lands over lands of a higher elevation in the district and benefited thereby.
ORS 547.470