The purpose of this study was to determine the persistence of 2,4-dichlorophenoxyacetic acid (2,4-D) applied to two lakes (one mesotrophic and one eutrophic) for the control of Eurasian watermilfoil (EWM), and to determine the impacts of 2,4-D on benthic macroinvertebrates in one of the lakes. One lake was treated with a liquid formulation, and the other with a slow release granular formulation of 2,4-D. Concentrations of 2,4-D in the water column were highest 1 and 2 days post-treatment and declined to below detection limits by 7 and 10 days post-treatment. We observed negative correlations between days post-treatment and taxa richness, and between days post-treatment and abundance of three of 12 taxonomic groups of macroinvertebrates. Lake managers need to balance control of EWM with possible impacts of 2,4-D to nontarget organisms.