This study dealt with the relationship between the characteristics of irrigation ponds and water quality. We conducted a statistical analysis of 556 irrigation ponds located in urbanized rural areas and flat rural areas throughout the country, and examined a number of indicators of water quality such as pH, chemical oxygen demand (COD), contents of total phosphorus (T-P) and total nitrogen (T-N). There were no strong correlations between the characteristics of the irrigation ponds and water quality. We then conducted a similar analysis of the ponds after classifying them into 4 groups based on hydraulic and meteo rological characteristics. In this analysis, a strong relationship was found for the water quality in each group of ponds. We also studied the nitrogen load in the effluent from the catchment basins and found that diffuse non-point-source nitrogen was the major constituent. Relative intensity of the factors affecting water quality was investigated by multiple regression analysis and box plot analysis.