The last hundred years humans have drastically changed the amount of available nitrogen in nature. Today human activities release twice as much available nitrogen as all natural processes are doing together. We also have degraded nature´s possibilities to take care of nitrogen through the draining of wetlands and straightening of rivers. In order to regain the potential of nitrogen retention in the water systems there now requires a reshape of the landscape we live in. A planned expansion of the mining activities in Garpenberg, Dalarna, would double the content of nitrogen in the waters below the mine. Water that already contains a high amount of nitrogen. To reduce the risk of eutrophication and increased pressure on the content of oxygen in the watercourses, in this study I investigate where a wetland with refine of nitrogen as a purpose can be located and constructed in the system of Forsån. By topographic studies one appropriate area where the river of Garpenberg flows past Krommetsbo is found. The potential of the area is supported by an inventory of species which are likely to colonize the wetland. The Krommetsbo-wetland will be able to contribute to the reduction of nitrogen in the lower parts of the system. However, additional measures are needed to change the situation in the upper parts of the system.