Technical Abstract: Drainage ditches are indispensable components of the agricultural production landscape. An environmental benefit of these ditches is mitigation of contaminants associated with agricultural storm water runoff (e.g. pesticides, nutrients, and sediments). In a controlled-release agrichemical runoff event, a 650 m drainage ditch effectively mitigated two commonly used pyrethroid insecticides, bifenthrin and lambda-cyhalothrin. For example, 3 h following the initiation of the storm runoff simulation, bifenthrin and lambda-cyhalothrin water concentrations ranged from 666 ug/L and 374 ug/L, respectively, at the inlet to 7.24 ug/L and 5.23 ug/L at 200 m downstream. No chemical residues were detected at the 400 m sampling site. A similar trend was observed throughout the first 7 d of the study where water concentrations were elevated at the front end of the ditch (0-25 m) and greatly reduced by the 400 m sampling site. Regression formulas predicted that bifenthrin and lambda-cyhalothrin concentrations in ditch water were reduced to 0.1% of the initial value within 280 m. Using mass balance calculations it was determined that the plant compartment was the major sink and/or sorption site for the rapid dissipation of bifenthrin and lambda-cyhalothrin from the water column. By 12 h into the study, the majority of the mass of each pesticide (>93%) was present in the plant compartment. For both water and plant compartments, there was a steady reduction of pesticide mass, while there was an enrichment and/or retention (relatively lower mass than in the plant compartment) of lambda-cyhalothrin in the sediment compartment over time. By incorporating current agricultural landscape features (i.e. vegetated drainage ditches) into a watershed management program, agriculture can continue to decrease potential non-point source threats to downstream aquatic receiving systems.