This study has shown that if pendimethalin enters water adsorbed to soil or sediment, little will desorb, and that which does reach water will rapidly degrade. Pendimethalin accumulated by snails was degraded (or lost) much more rapidly than that accumula- ted by fish. Accumulation patterns indicate that a complex relationship exists between the metabolites found in water and organisms. The rapid degradation of pendimethalin suggests that it poses little danger to the aquatic environment.