Spatial redistribution of legacy mercury (Hg) contamination in the Hackensack River estuary (New Jersey, USA) was evaluated using mercury stable isotopes. Total Hg varied from 0.06 to 3.8 mu g g(-1) in sediment from the tidal Hackensack River and from 15 to 154 mu g g(-1) near historically contaminated sites in upper Berry's Creek, a tributary of the Hackensack River. delta Hg-202 values for total Hg from Berry's Creek and Hackensack River estuaries varied over a fairly narrow range (-0.44 parts per thousand to -0.21 parts per thousand), but were highest for sediment from upper Berry's Creek. Isotope mixing plots show that residual legacy mercury from upper Berry's Creek is partially diluted by a low concentration and low delta(202) Hg pool of mercury associated with low organic matter content sediments similar to those in Newark Bay. Based on an isotope mixing model, we estimate that upper Berry's Creek contributes 21%-82% of the mercury in sediments in the Hackensack River estuary and its tidal tributaries, including upstream marsh habitats far from the primary source. Our results show that mercury stable isotopes can be used to track the redistribution of mercury in tidal ecosystems and highlight the potentially large areas which may be affected by legacy mercury contamination in estuaries.