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This study examined the relationship between the land-use and land-cover changes in the mountainous Haean Basin of the Republic of Korea, a water source area, and the muddy water in the downgradient. The water flowing out from the basin is highly turbid having value of 650.1 Nephelometric Turbidity Unit (NTU), while that from the upper Inbuk Stream lacking major crop fields is very clean (less than 1 NTU), indicating agricultural activities as the origin of the turbid water. Among the six major crops in the cultivated area, rice prevails the maximum area (31.5-51.5%, mean = 38.7%), followed by radish (0.2-32.4%, mean = 20.1%) and potato (9.4-32.2%, mean = 19.4%). The mean annual soil erosion (t ha(-1)yr(-1)) from major crops; radish (55.6), potato (53.0), cabbage (47.9), soybean (40.3), ginseng (23.6), orchard (18.7), and rice (1.3) contributed to water turbidity, differently. Avoiding the cultivation of radish crop can help to reduce overall rate of soil erosion from the basin. Proper maintenance of mitigation measures would result in minimal soil erosion and reduced water turbidity.