IOWA CITY (AP) — Wastewater treatment and industrial plants would be asked to make costly upgrades to cut pollution while farmers would do so voluntarily under a long-awaited strategy released Monday to reduce harmful nutrients in Iowa waterways and the Gulf of Mexico.

Gov. Terry Branstad’s administration released the 200-page document laying out plans to tackle one of Iowa’s most pressing environmental issues, after two years of study and private meetings. It comes in response to the U.S. Environmental Protection Agency’s order in 2008 for 12 states along the Mississippi River to develop strategies to prevent nitrates and phosphorous from reaching the Gulf of Mexico, where excess levels of the substances make large areas unsuitable for marine and plant life.

Iowa is a leading contributor to the problem, which comes from runoff caused by fertilizers and manure used on farm fields and at wastewater and industrial plants.