DES MOINES, Iowa — The Iowa Supreme Court has ruled against Des Moines Water Works in its attempt to pursue damage payments from northwest Iowa counties it says allowed polluted water to move from farm fields into the Raccoon River.

The court released its ruling Friday morning. Water Works had sued Calhoun, Buena Vista, and Sac counties for letting nitrates from field fertilizer to flow down the Raccoon River, where they had to be removed in an expensive process costing Water Works millions.

In the ruling, the court explains “drainage districts have a limited, targeted role—to facilitate the drainage of farmland in order to make it more productive. Accordingly, Iowa law has immunized drainage districts from damages claims for over a century. This immunity was reaffirmed unanimously by our court just over four years ago.”

Read the entire ruling here.