Unit the 1950s Lake Maggiore exhibited the characteristics of oligotrophy with low to concentrations of inorganic N and P, and low levels of primary productivity (Roggiu et nutrie cultural al., 1985). However, cultural eutrophication of the lake accelerated rapidly after the late 1950s. Total P concentrations in the lake water increased to 30-35 mg 3 during 1976-77 and concentrations of nitrate-N increased twofold (Roggiu Prou et al., 1985). Over a threefold increase in phytoplankton production was observed by the mid-1970s, and nuisance Lak app blooms of cyanobacteria also occurred (de Bernardi et nia al., 1996). Mosello and Ruggiu (1985) subsequently par applied the OECD (1982) modeling framework in to assess water quality restoration strategies for the the lake, and they concluded that a 67% reduction in an external P loading would be required to return Lago tra Maggiore to oligotrophic conditions. Marked improvements in water quality have occurred pe in recent years, and the reversal of eutrophication has continued to the These present. improvements can be attributed to the construction of sewage treatment p plants that serve 60-70% of the total population in the drainage basin, which has caused dramatic reductions in nutrient loadings to the lake. In addition, further reductions in P loading have occurred as a result of restrictions in the use of P-containing detergents, as well as reduced industrial activity that followed an industrial crisis in the 1980s. Epilimnetic concentrations of total P have subsequently declined threefold to ca. 10 mg m and a parallel decrease has occurred in algal biomass as measured by concentrations of chlorophyll a (de Ber nardi et al., 1996). Phytoplankton species diversity also increasing, with major changes in the relative abun dance of diatoms and cyanobacteria