Chlorophyll a concentrations in Lake Pearl, Florida, increased as the percentage of the lake's total volume infested with aquatic macrophytes decreased. Using data from 32 Florida lakes having a wide range of limnological characteristics, we demonstrated that predictions of chlorophyll a concentrations could be improved by including a term for the percentage of the lake's total volume infested with macrophytes in existing nutrient–chlorophyll models. Our best-fit multivariate regression equation waswhere CHLA is the chlorophyll a concentration (milligrams per cubic metre), TN is the total nitrogen concentration (milligrams per cubic metre), TP is the total phosphorus concentration (milligrams per cubic metre), and PVI is the percentage of the lake's total volume infested with macrophytes. By use of this equation, we assessed the potential effect of aquatic macrophytes on chlorophyll yields and Secchi disc transparencies in lakes of different trophic status.