This article presents the impact on waterbirds in Doñana National Park (Spain) of an accidental release of 5 million m3 acid waste produced by the processing of pyrite ore. Heavy metals (zinc, copper, cadmium, and lead) and arsenic were measured in several soft tissues (liver, kidney, and muscle) taken from 14 waterfowl species collected between April 1998 and May 2000. The main source of copper and zinc found in the waterfowl species examined was the spill waste, whereas cadmium, lead, and arsenic could also came from other sources. Kidney was the primary organ for cadmium and lead accumulation, whereas liver accumulated the most zinc and copper. Arsenic was concentrated in both muscle and liver tissue. The degree of contamination of the area where the birds lived, their age, their sex their size, and the time since the spill were found to have less influence than species and trophic level on the accumulation of metal in organs and tissues. Four species (Anser anser, Ciconia ciconia, Larus ridibundus, and Porphyrio porphyrio) were found to have the highest levels of the 5 elements.