Ž . The Science of the Total Environment 213 1998 279290 Development of fish mercury concentrations in Finnish reservoirs from 1979 to 1994 P. Porvari  Finnish En ironment Institute, Impacts Research Di  ision, P.O. Box 140, FIN-00251 Helsinki, Finland Abstract Ž . Ž . Ž . Ž . Mercury Hg concentrations in burbot Lota lota , perch Perca flu iatilis , northern pike Esox lucius , roach Ž . Ž . Ž . Rutilus rutilus , whitefish Coregonus la aretus and peled C. peled were monitored in 18 reservoirs situated in Ž . western and northern Finland over a period of 16 years 1979  1994 . The reservoirs were impounded from 1964 to 1980. The surface areas ranged between 1 and 417 km 2 . Data from downstream sites and reference lakes were compared to reservoir mercury data. Generally, fish Hg concentrations in reservoirs exceeded those in natural lakes. Shortly after inundation, fish mercury concentrations clearly increased and remain 15  25 years above background concentrations. The mean Hg concentrations in standardized 1 kg pike from 1989 to 1993 was 0.45 mgkg in natural lakes and 0.58 mgkg in reservoirs. The 1 mgkg fish Hg level recommended by health authorities as the upper limit Ž for human consumption was still exceeded in two reservoirs 20 years old or more. The two largest reservoirs 24 and . 27 years old in 1994 with significant commercial fishing had Hg levels below 0.5 mgkg in all fish species studied. Statistical models for predicting the Hg concentrations in the weight standardized pike were verified with the Ž . observed data. For most of the reservoirs, predictions from models based on pH, organic matter COD in water, the Ž extent of water level regulation and reservoir age agreed well with observed data. In the most southern, new under . 20 years old and heavily regulated reservoirs, pike Hg concentration followed a logarithmic function of reservoir age. Ž . Model predictions of mercury in pike in the planned Vuotos reservoir in northern Finland predicted that Hg would exceed 1 mgkg Hg for the first 12 years after the flooding.  1998 Elsevier Science B.V. Keywords: Mercury; Methylmercury; Accumulation; Reservoir; Fish  Tel.:358 9 403000; fax: 358 9 40300390; e-mail: petri.porvari@vyh.fi 0048-969798$19.00  1998 Elsevier Science B.V. All rights reserved. Ž . PII S0048-9697 98 00101-6