The National Lake Survey (Table 4, #7.4) gives an aerial coverage of water quality in Swedish lakes. Water samples are taken at 0.5 to 2 m depth in a total of 1841 lakes in northern Sweden in a 6-year rotation with about 350 lakes per year. The samples are taken after the lake’s complete overturn in the autumn. For water chemistry the samples are analyzed for 20 variables (temperature, pH, NH4, NO2+NO3, Tot-N, Tot-P, PO4, TOC, Si, absorbance, Fe, Mn, alkalinity, Ca, Mg, K, Na, SO4, Cl and F) and less frequently for 9 trace metals (Cu, Cd, Pb, Cr, Ni, Co, Ni, V, Al). In the Trend Lakes program the sampling is more frequent (4 times per year for water chemistry and one time per year for bottom fauna, phytoplankton and macrophytes). The aim of the program is to build time series to detect environmental changes due to e.g. Climate change or large scale changes in deposition load. In this program about 40 lakes are sampled in northern Sweden. For water chemistry the samples are analyzed for the same elements as in the National Lake Survey. In addition test fishing is conducted in 2 of the lakes per year. Invented variables: Temperature, pH, NH4, NO2-NO3, Tot-N, Tot-P, PO4, TOC, Si, Absorbance, Fe, Mn, Alkalinity, Ca, Mg, K, Na, SO4, Cl, F, and trace metals Cu, Cd, Pb, Cr, Ni, Co, Ni, V, Al Sampling depths: Sampling at 0.5 - 2.0 m depth during fall circulation Network layout: The network is based on EMEP-squares and gives between 19 and 134 lakes sampled per county every year. Sampled lakes rotation: About 350 lakes are sampled in northern Sweden every year in a six-year -periodical program. Out of 4824 lakes sampled in the country 2112 are situated in northern Sweden.