Surface waters in rapidly developing areas are particularly vulnerable to anthropogenic contamination from both point and nonpoint sources. Runoff and shallow groundwater flow from agriculture, suburbia and industrial sites commonly results in higher concentrations of heavy metals and nutrients to nearby waterways. Mill Creek, a tributary of the Fox River in northeastern Illinois, has a drainage basin area of approximately 80.3 km², with a channel length of approximately 25.7 km. Parts of the watershed have experienced rapid development in the past several decades, and as a result, the system now drains agriculture areas, suburbia, forests, wetlands, and lakes. Hydrographs from a gauging station near the confluence of Mill Creek and the Fox River show that discharge peaks relatively quickly after large rain events, with lag times typically ~16 hours. Mill Creek shows signs of significant bank erosion during high flow events. The purposes of this study are: 1) to determine if there is a predictable relationship between discharge (and gauge height) and contaminant concentrations, and 2) to identify point sources of pollution. The contaminants studied include: P⁺, Cu²⁺, NO^3-, Fe³⁺, Pb²⁺, Hg²⁺, and As³⁺. The pH was measured at sample sites, as well. This study found most of the highest contaminant concentrations in low-flow (baseflow) conditions, suggesting contaminants enter the system via the shallow groundwater system. While storms may wash significant quantities of contaminants into the system, they tend to be diluted, and they flow through the stream system fairly rapidly. The contaminants of highest concern include: NO^3-, Pb²⁺, As³⁺ and Hg²⁺ due to their environmental impacts and relatively high concentrations. There are no EPA standards for nitrates, but high averaged concentrations of 1.8-6.9 ppm were found. The highest concentrations of arsenic (1.3 ppm), lead (4.6 ppm), and mercury (2.2 ppm) all exceeded EPA standards of 0.34 ppm , 0.065 ppm, and 0.0014 ppm, respectively. Downstream variations indicate contaminant sources from both agricultural and suburban areas, although no point sources were identified.