The Fox River Basin (fig. 1A) spreads over multiple counties. Several of these counties, such as McHenry and Kane Counties in Illinois and Waukesha County in Wisconsin, are undergoing rapid urbanization and consequent stresses on their water-supply systems (CH2MHill, 2002; Groschen and others, 2004; Kay and others, 2006; Meyer and others, 2009). Water-quality considerations that affect groundwater supplies also in some instances complicate the outlook for a sustainable water supply. The city of Waukesha, for example, in the face of radium exceedances in wells tapping the deep Cambrian- Ordovician aquifer system, is evaluating alternative sources of water such as increased withdrawals from shallow wells and a possible diversions from Lake Michigan (Southeastern Wis- consin Regional Planning Commission, 2010). Other commu- nities in the Fox River Basin are likely to face similar choices in efforts to augment their water-supplies in coming years. The possibility that shallow pumping will be increased throughout the basin could imply decreased base flow to the Fox River and its tributaries and increased stresses on lakes and wet- lands, especially in the context of uncertain climate trends.