Industrial effluents discharged into the environment may have ecotoxic effects even if they come up to regulatory standards. Chemical evaluation of treatment performance by end-of-pipe treatment systems is thus not sufficient, especially when mixtures of metallic and organic contaminants are concerned. Given that contamination may alter biological characteristics of the environment, biomonitoring studies may provide information on integrated ecotoxical effects. However, there is a need for bioassays purpose-designed for direct use at industrial sites. Many biomonitoring tools already exist and have been proved to be efficient for evaluating the ecotoxicity of contaminated waters, but most of them require laboratory equipment. In this study, an experiment in microcosms under controlled conditions of pollution was carried out to assess the morphological responses of five helophytes exposed to mixtures of organic and/or metallic pollutants. The criteria of plant growth and development, i.e. aerial elongation and leaf senescence, that were the most relevant for reflecting the ecotoxicity of contaminant mixtures and that could be monitored on-site with a user-friendly method, were then selected. Focusing on these selected criteria, a new bioindicator tool, named the Helophyte Development Index (HDI), was created. Our results suggest that the HDI is a promising tool to use on-site for assessing the ecological state of waters released in aquatic environment by industrial factories, following the recommendations of the European Water Agency. (C) 2015 Elsevier B.V. All rights reserved.