Abstract: Paddies in the river network area in plains of southern China produce large amount of drainage discharge in the growing season. Pesticides applied to the paddy fields can be observed in adjacent drainage ditches as they traveled with surface and shallow subsurface drainage, or deposited with the wind drift when they are not thoroughly degraded right after application. Consequently, the surrounding water bodies including the drainage ditches and ponds would be contaminated by the pesticides, which poses a potential threat to the aquatic ecological environment. Based on a field monitoring study in the Farmland Water Conservancy Scientific Research Station of Jiangdu District, Yangzhou, China, we conducted high-frequency (with the shortest sampling interval of 1 h) and short-term (3-day duration) sampling in the upper and middle sections of drainage ditches, surface water and ground water in paddies right after pesticide application. The concentrations of chlorpyrifos (CPF) and abamectin (ABM) (two commonly used paddy insecticides) were analyzed. The results showed that peak concentrations appeared twice within 5 h after application in the adjacent drainage outlet for both insecticides; the peak concentrations of CPF and ABM were 0.33 mg/L and 4.60 μg/L, respectively in the field ditch, the peak concentration of CPF was much higher than the acute water quality criteria of CPF in the Yangtze River delta region (0.013-0.112 μg/L). Concentrations of the two insecticides decreased rapidly when there was no outflow in the field ditch, indicating that controlled drainage might have a great impact on the concentration variations in ditches. The concentrations of CPF and ABM were much lower in ditches between 36 and 72 h after their applications; CPF concentrations varied from 0.007 to 0.020 mg/L and ABM concentrations were lower than 0.1 μg/L. Concentrations of CPF in the water bodies around paddies decreased in the order of the field ditch (0.007-0.33 mg/L) to surface water of paddies (0.004-0.050 mg/L), and then to ground water of paddies (0.000 6-0.002 mg/L). A time lag was observed for the concentration variations in different sites of the field ditch. When pesticides application was based on the recommended dose for paddies (80 g per 667 m2 for CPF, 50 mL per 667 m2 for ABM), CPF had high to extremely high risks to majority of the concerned aquatic animals, while ABM had only low to medium risks to the most aquatic animals. CPF had extremely high risks to 8 out of 16 fishes and high to extremely high risks to 5 different shrimps or crabs. ABM had low to medium risks to 16 out of 19 fishes and low risks to 3 shrimp or crab species. The safe concentrations of CPF calculated with two methods were 1.2×10-5-0.384 9 mg/L and 6×10-6-0.194 0 mg/L, respectively. The environmental exposure concentration of CPF in paddies after pesticide application was larger than the safety concentrations of most evaluated aquatic animals, while different results were obtained for ABM. Results from this study indicate adverse environmental and ecological effects of the monitored insecticides application in paddies; they may provide valuable scientific reference for ecological risk management of pesticides and agricultural non-point source pollution control.