There is current interest in the use of artificial wetlands and macrophyte-cultured ponds for the treatment of agricultural drainage water, sewage, and industrial effluents. Aquatic plant-based water treatment systems have proved effective and economical in improving the quality of wastewaters containing excess nutrients, organic pollutants, and heavy metals. This investigation was conducted to test the hypothesis that herbicide-tolerant aquatic plants can remediate herbicide-contaminated waters. The addition of Ceratophyllum demersum (coontail, hornwort), Elodea canadensis (American elodea, Canadian pondweed), or Lemna minor(common duckweed) significantly (p < 0.01) reduced the concentration of [14C]metolachlor (MET) remaining in the treated water. After a 16-day incubation period, only 1.44%, 4.06%, and 22.7% of the applied [14C]MET remained in the water of the surface water systems containing C. demersum, E. canadensis, or L. minor whereas 61% of the applied [14C]MET persisted in the surface water systems without plants. C. demersum and E. canadensis significantly (p μ 0.01) reduced the concentration of [14C]atrazine (ATR) in the surface water. Only 41.3% and 63.2% of the applied [14C]ATR remained in the water of the vegetated systems containing C. demersumand E. canadensis, respectively. Eighty-five percent of the applied [14C]ATR was detected in the water of the L. minor and nonvegetated systems. Our results support the hypothesis and provide evidence that the presence of herbicide-tolerant aquatic vegetation can accelerate the removal and biotransformation of metolachlor and atrazine from herbicide-contaminated waters.