Ecological risk assessments employ mathematical fate and transport models to estimate pesticide concentrations in the environment. Results are highly based upon input data, yet the sensitivity of such models to specific parameters is unknown. The purpose of this study is to investigate the sensitivity of one such model, TPQPond (Haith, 2010), a model of pesticide runoff and subsequent accumulation in a receiving pond from various types of grass surfaces. The analysis was based on one-in-10 year maximum pond concentrations of 38 different pesticides from 100 year simulations. The simulations were conducted for nine geographic locations and three golf course surface types. These concentrations are then compared to toxicity endpoints of target species (invertebrates, fish, plants, and algae). Seven input parameters were modified in order to create a range of values over which calculated risk quotients could be compared to the original values. It was determined that the model was most sensitive to changes in pond depth and turf organic carbon content. It was moderately sensitive to pond half life and turf organic carbon content values and mildly sensitive to changes in the application dates. Changes in values for minimum pond volume did not affect the calculated risk quotients, and, due to the high carbon content, both high and low modification of total suspended solids led to decreases in risk quotients. Based on these findings, it is important to choose values for input parameters carefully for a given risk assessment as small changes in parameter values that the model is sensitive to can have significant impacts on the results of the assessment.