Neutron activation analysis has been used to analyze sediment cores from the Rock River and two branches of Kent Creek, one of its tributaries, to determine the concentrations of thirteen heavy metals (Ti, Cu, V, Mn, As, Sb, Se, Cr, Ni, Sc, Fe, Zn, and Co) and two rare earths (Sm and La). The downstream sites of both the Rock River and the two branches of Kent Creek have elevated concentrations of several heavy metals including arsenic, antimony, and zinc. In addition, hundreds of parts per million of copper have been found in samples from the downstream site of the North Fork of Kent Creek. Toxicity tests of the sediment also indicate that the downstream sites are detrimental to lifeforms. Analysis of the data from the two branches of Kent Creek clearly indicate that heavy metal concentrations increase as the distance from the center of industrial activity (Rockford) decreases.