Water is supplied in the Greater Istanbul Metropolitan Area from the surface water of six main reservoirs. The present land use in the catchment areas of the reservoirs indicates that the area devoted to agricultural activities and to forests and meadows varies between 73 and 97% and that only a minor percentage, 1-26%, is devoted to settlements and industries. In contrast to the land use profile, the current environmental evaluation of the catchment areas reveals that point sources dominate over diffuse sources. However, this trend is expected to be reversed in the near future, making diffuse sources and control of fertilizers and pesticides the most significant issue. Pollutant loads regarding pesticides and fertilizers are calculated from unit loads based on area. These pollutants are observed to have a negative impact on water quality in terms of eutrophication and toxicity. In this paper, the status of fertilizers and pesticides are addressed and some protective measures for reducing the impact of agricultural pollutants in the reservoirs are recommended.

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