A MODFLOW-NWT groundwater flow model was developed to simulate groundwater movement in the area around Anvil Lake, and groundwater inputs and outputs from the lake from 1980 to 2014. Surface-water hydrology was simulated using the lake package. The MODFLOW model was first calibrated for steady-state conditions, or "average" conditions corresponding to January 1, 1980, to December 31, 2014 to estimate spatial hydrogeologic properties. Following the steady-state calibration, the model was applied in transient mode to estimate average monthly hydrologic conditions (groundwater inputs and outputs) for each year from 1980 to 2014.