With the growing concern about elevated phosphorus concentrations in lakes, rivers, and streams, scientists must investigate factors contributing to phosphorus transport from the landscape. The phosphorus flux from nonpoint sources, particularly land applications of poultry litter and other animal manure, are closely related to the production and location of surface runoff. Daily stream discharge and the software program, Base Flow Index (BFI), were used to estimate the production and temporal patterns of surface runoff at different locations within the Illinois River watershed, including selected tributaries in northwest Arkansas and northeast Oklahoma. Daily stream discharges from approximately ten U.S. Geological Survey Gauging Stations were imported into BFI to estimate base flow by identifying minimum stream flows within given time periods. The software was parameterized using a minimum time period of five days and a turning point factor of 0.5. Surface runoff was found to be greatest during the rainy spring and wet winter seasons, and least during the dry summer and early fall seasons. Land applying poultry litter and other animal manures could pose less risk of transport during the drier summer and early fall months, likely helping to minimize nonpoint source phosphorus loads introduced into the Illinois River.