Geographic Information Systems (GIS), computer systems which can analyze mapped information, can help reduce nonpoint source pollution in the Lake Superior basin by providing researchers and managers with a tool for predicting the consequences of land use change. In an EPA-funded study of 15 watersheds in the Twin Cities metropolitan area, researchers at the Natural Resources GIS Laboratory (NRGIS) determined how wetlands and other land uses affected water quality. They found that wetlands were important to water quality at the watershed scale, so land use changes which would destroy wetlands could degrade downstream water quality. They also found that the position of the wetlands in the watershed made a difference as to how they affected downstream water quality, a relationship which would have been difficult to detect without the use of a GIS.