The objective of this study is to investigate water quality of lake and to provide data for management practices of water quality measurement network in Chungcheongnam-do. 100 Samples of lakes was collected and analyzed. Variation degree of water contamination and changing trend of lake water for the samples were considered focussed on COD. The obtained results were as follows; 1. As a analytical results to water contamination, COD concentration for 28 lakes in 8 cities exceeded 8.0㎎/L so that it was evaluated these water can't help using farming water. 2. All lakes in Gongju and Cheonyang region was suitable for agricultural water as 3th class of water quality standard, 9 out of 12 lakes in Taean was short of the quality of agricultural water standard, and 3 lakes in Dangjin was serious contaminated under the regular grades. 3. There was no lake water fitted to 1 grade class of environmental standard of lake water quality in korea, only one lake suitable to 2 class, 48% for 3 class, 21% for 4 class, 16% for 5 class and 12% under the grade. So it was become that water quality of most lakes in Chungcheongnam-do was contaminated.