Polychlorinated naphthalene (PCN) concentrations and fluxes were measured in a dated core from the profundal sediments of Esthwaite Water, a seasonally anoxic semirural lake in northwest England. The vertical profile shows that the ΣPCN flux remained fairly constant at 0.4−0.6 μg m-2 y-1 from depth until the early 1940s, escalating sharply thereafter to a subsurface maximum of 12 μg m-2 y-1 in the late 1950s to mid-1960s followed by a 4-fold decrease to the sediment−water interface. The ΣPCN maximum predates the ΣPCB maximum by 20 years, broadly consistent with the time lapse in the production and wide use of both compounds. Furthermore, there was a secondary peak in the profiles of both compound classes corresponding to the period of maximum input of the other compound class. This may be a result of PCNs present as impurities in the manufacture of PCBs and vice versa. The vertical profiles of the individual PCN homologue groups closely followed that of the ΣPCN profile with no overall change in the mass percent contribution of individual PCN congeners throughout the core. To our knowledge, this is the first study to reconstruct the historical record of PCNs in the environment.