Typha latifolia is an aggressive rhizomatous emergent wetland plant that can invade wetlands resulting in near monotypic Typha stands. T. latifolia is also one of the most commonly used macrophyte species in constructed wetlands. The hypothesis that elevated nitrogen and phosphorus concentrations observed in nonpoint source runoff increases T. latifolia fitness and potentially T. latifolia invasiveness was tested under semi-controlled laboratory conditions. A protocol was developed to propagate T. latifolia from seed in low P sediment to simulate an oligotrophic pre-impact reference treatment. Microcosms provided with hypereutrophic levels of P combined with oligotrophic or eutrophic levels of N had significantly greater shoot biomass and maximum leaf height compared to oligotrophic N and P treatment microcosms. These results indicated that high P often found in runoff may contribute to T. latifolia invasion. We recommend that noninvasive species of macrophytes be used in constructed wetlands to prevent impact to ecologically sensitive areas.