The research project involved laboratory and field investigations. The northern lakes--field study was conducted by Environmental Control Technology Corporation, Ann Arbor, Michigan. The southern lakes--field study was conducted by Environmental Science and Engineering, Inc., Gainesville, Florida. To achieve the project objective four ponds were subjected to outboard engine emissions at a rate calculated to be three times greater than that from saturation boating levels. Some marginal changes in the lakes biota were noted but the differences were such that it is not certain whether they were from natural or stress effects. As a result it was not possible to determine conclusively the precise point at which outboard emissions effect the aquatic environment. Based on the results, it is plausible to conclude, however, that because of the high stress levels employed in this study, outboard motor emissions do not significantly affect aquatic ecosystems.