Questions concerning the effects of drainage, peat mining and timber harvesting on streamflow response in the northern Lake States of the U.S.A. led to the development of the Peatland Hydrologic Impact Model (PHIM). PHIM is a generalized, deterministic, continuous simulation model, that is physically-based to the extent possible. Three independent landtype submodels represent watershed conditions common in the region. The appropriate land-type submodel(s), either natural peatland (NWATBAL), mined peatland (MWATBAL), or mineral soil upland (UWATBAL) are configured by the model user to represent the watershed. The submodels were applied to test the model on the streamflow response from three different peatland watersheds. Stormflow events were simulated for a 3,758 ha natural peatland and a 155 ha mined peatland. Annual water yield simulations for a 9.72 ha upland-peatland watershed produced a mean ratio of predicted/observed streamflow of 1.01 ± 0.08 for six test years. The model is generalized so that it should be adaptable to similar physiographic regions with minor modifications.