The 48 hectare Lake Josephine was being impacted by urban stormwater runoff flowing directly into the lake from 237 hectares of its 341 hectare watershed. Runoff from 90 hectares — or 37 percent — of this direct drainage area was diverted to a 12 ha wetland treatment system for pretreatment prior to its discharge into Lake Josephine. The first year three monitors revealed the treatment system had removal efficiencies of 62 percent for total phosphorus, 69 percent for orthophosphorus, 48 percent for total Kjeldahl nitrogen, and 79 percent for total suspended solids. Three-year average water quality data from the lake itself was also compared to data obtained for 3 years prior to the diversion. The comparison revealed that after the diversion, total phosphorus concentrations decreased from .092 to .058 mg/l, total Kjeldahl nitrogen concentrations decreased from 1.25 mg/l to .7 mg/l, ortho-phosphorus concentrations decreased from .038 mg/l to .03 mg/l, and Secchi depth transparency increased from 3.83 meters to 5.0 meters.