In this study, we investigated the effect of herbaceous planting richness on the physicochemical parameters of water temperature, pH, and dissolved oxygen in created wetlands. Mesocosms were planted with common wetland plants along a gradient from zero species to four species and observed over three growing seasons. Aboveground biomass was harvested after the second growing season to simulate disturbance. Planting richness was not found to directly influence any of the parameters. Instead, it seems that algae were more influential on observed changes to pH or dissolved oxygen than the macrophyte. Traditionally, monitoring of mitigation wetlands focuses on growth of macrophytes (e.g. cover percentage) and eschews the importance of the algal community in water quality function. Our results suggest that inclusion of simple, low-cost measures of water physicochemical parameters in mitigation site performance monitoring may contribute to a better assessment of ecosystem function development in newly created mitigation wetlands. Further study is necessary to quantitatively assess the relationship, if any, between the physicochemical parameters of water quality and nutrient retention performance that is rarely evaluated in mitigation wetlands.