ABSTRACT:A modeling framework was developed to determine phosphorus loadings to Lake Okeechobee from watersheds located north of the lake. This framework consists of the land‐based model CREAMS‐WT, the in‐stream transport model QUAL2E, and an interface procedure to format the land‐based model output for use by the in‐stream model. QUAL2E hydraulics and water quality routines were modified to account for flow routing and phosphorus retention in both wetlands and stream channels. Phosphorus loadings obtained from previous applications of CREAMS‐WT were used by QUAL2E, and calibration and verification showed that QUAL2E accurately simulated seasonal and annual phosphorus loadings from a watershed. Sensitivity and uncertainty analyses indicated that the accuracy of monthly loadings can be improved by using better estimates of in‐stream phosphorus decay rates, ground water phosphorus concentrations, and runoff phosphorus concentrations as in