The objective of this study was to determine if the runoff from croplands fertilized with municipal sludge was toxic to aquatic biota and, therefore, a potential threat to either public health or the environment. Seven-day bioassays with Ceriodaphnia dubia showed that the No-Observed-Effect-Concentration (NOEC) was 24 g/L and the Lowest-Observed-Effect-Concentration (LOEC) for survival was 30 g/L for soil samples treated with 35.2 metric tonnes (MT)/ha of municipal sludge. For soil samples treated with 0 and 17.6 MT/ha of sludge, the survival rates of C. dubia were not significantly affected at concentrations of 6-30 g/L of soil. Reproduction was suppressed by 25% when daphnids were exposed to 3.3 g/L concentration of soil treated with sludge at 35.2 MT/ha. A 50% suppression of reproduction occurred when daphnids were exposed to 15 g/L concentration of soil treated with sludge at 17.6MT/ha. A sludge application rate of 17.6MT/ha suppressed reproduction at a treatment concentration of 18g/L. These data indicate that the runoff from agricultural lands treated with municipal sludge has the potential to affect reproduction in daphnids and, therefore, the environment through the aquatic food chain.