DES MOINES, Iowa (AP) — The Des Moines Water Works board has voted unanimously to sue three northern Iowa counties, holding them responsible for the high nitrate levels the in rivers the utility uses for source water.

The five-member board says it will file a notice of intent to sue Calhoun, Buena Vista and Sac counties because they oversee 10 drainage districts that were designed to move water out of farm fields downstream. The suit will allege with water the drainage districts move contaminants like nitrate that Water Works must remove when the levels exceed U.S. Environmental Protection Agency limits.

A notice of intent will be Friday which informs the county supervisors and state officials that a lawsuit will be filed in 60 days. The process is laid out in the federal Clean Water Act.