For two decades, fish tumour surveys have been used to monitor habitat quality in the Chesapeake Bay ( USA ) watershed. Tributaries with sediments contaminated with polynuclear aromatic hydrocarbons ( PAH s), known to cause liver neoplasia, were frequently targeted. Here, we compare surveys in brown bullhead Ameiurus nebulosus conducted in 2009–2011 in the tidal Potomac River watershed (including the Anacostia River) with prev...