This project investigates the toxicity of sidewalks and parking lots through a bioassay using a living organism. The Daphnia magna, a common water flea, is used to measure the toxicity of sidewalks and parking lots. Their heart rate and deaths are measured to determine the impact our infrastructure has on the D. magna. Since the D. magna are primary consumers, a large portion of the aquatic ecosystem in local ponds and streams is dependent on these organisms for food. In the experiment the organisms were separated into three different groups: control, simulated sidewalk run-off water, and simulated parking lot run-off water. Each of the three groups had an initial amount of 20 D. magna, and a total of three trials were conducted each lasting 72 hours. The heart rates and deaths were measured every 12 hours. Although the overall result for the number of D. magna alive in each cup for the experiment proved insignificant, the individual trials provided statistically significant results on the effect of the sidewalk and parking lots on the organisms.