The objectives of this paper are to characterize an "ideal" environmental impact assessment (e.i.a.); to review the contemporary status of e.i.a. for several major activities and areas of development; and to identify successes, failures, and future needs in e.i.a.The institutional procedures to be followed for e.i.a. have been formalized in a number of countries, but the scientific basis and methods are still developing. We propose that the following elements comprise an ideal e.i.a.: (1) definition of scientific objectives, (2) background preparation, (3) identification of main impacts, (4) prediction of effects, (5) formulation of usable recommendations, (6) monitoring and assessment, (7) sufficient lead time, (8) public participation, (9) adequate funding, and (10) evidence that recommendations were used.The "best available" predictive, preoperational e.i.a.'s involving aquatic resources (power plants, fossil fuels, recreation, reservoirs, wastewater treatment, forestry, and dredging and water diversion in estuaries) were reviewed and scored on a 0–5 scale for each of the elements identified above. Mean scores for the criteria which could be assessed (nos. 1–8) indicated that the quality of the best available e.i.a.'s does not exceed our defined average but improves when legally required documents are excluded from the calculations. The lowest means, for criteria within the scientist's control (nos. 1–5), were obtained for "Prediction of effects" and ' "Formulation of usable recommendations." Overall mean scores for each development area (criteria 1–5) indicated three broad groups which included studies of above average quality (wastewater treatment, recreation); studies of approximately average quality (estuarine impacts, power plants, reservoirs, and fossil fuels); and studies of below average quality (forestry practices).Environmental impact assessment has had the following successes: increased environmental awareness due to public involvement in e.i.a., some environmental protection, and elucidation of intriguing research problems. The list of failures of e.i.a. is, however, longer: "tokenism," unrealistic time constraints, uncertainty of program or development schedules, difficult access to e.i.a. literature, questionable ethics, lack of coordination among studies, and poor research design.Future organizational/administrative needs of e.i.a. include improved access to e.i.a. literature, increased accountability for e.i.a.'s and their authors, improved public input into project decisions and designs, and improved organization and presentation of e.i.a. reports. Future scientific/research needs include development of methods to define and quantify relationships between biological, esthetic, and economic impacts; support for independent biological inventory programs; adequate time frames; improved design of research; inclusion of monitoring and assessment in every e.i.a.; study of cumulative impacts on a regional or national scale; and improved communication between scientists and planners.Key words: environmental impact assessment, aquatic ecology, power plants, fossil fuels, recreation, reservoirs, wastewater treatment, forestry, dredging and water diversion (estuaries)