MISSOULA, Mont. -

A few hundred yards west of the intersection of Mullan Road and Clark Fork Lane in Missoula is an entrance to what appears to be an empty field. They're hard to spot now, but in that field are 72,000 poplar trees, with another 24,000 being planted in the near future.

It's the realization of 12 years of work by the city of Missoula to keep more of its wastewater out of the Clark Fork River. The Missoula water treatment plant currently releases 10 million gallons into the river each day.

The water is treated, but the plant can't remove nitrogen and phosphorus. The pollutants promote algae growth, which can take so much oxygen from the water that fish die of suffocation. Nitrates and phosphorus are also essential ingredients in plant fertilizer.

The city saw an opportunity, and after an initial test project they leased land to divert up to 20 percent -- 1.5 millon gallons of water -- to irrigate what will ultimately end up being 98,000 trees on 180 acres of land.

The additional nutrients mean that the trees will grow from 3 inches to over 3 feet by the end of the fall season. As the trees mature, they will grow between 6 and 10 feet taller each year.

The project is scheduled to run for 16 years, with timber harvesting of the trees beginning in the 12th year -- 2026.  The trees will produce thousands of feet of lumber and tons of compost material, repaying the initial investment from the city in timber sales.

City managers hope that this project can expand to other properties. The trees may be able to take even more water than projected, so studies will continue during the first years of the project.