The St-Lawrence River is an essential waterway for North America and is exposed to many anthropogenic stresses such as industrial and municipal wastewater or by the agricultural activities. This study is a part of a large research project aiming at developing an ERA tiered framework for sediment management, in the context of integrated management of contaminated sediment, site restoration and sustainable navigation. The purposes of this part of the study are to develop traits approach for the St. Lawrence River and to assess sediment quality by exploring the relationships between chemical contamination and benthic community structure using traits approach. During falls 2004-2005, macroinvertebrates were collected in 59 sites in the St. Lawrence River, especially in its three fluvial lakes and in the harbour zone of Montreal. Organic (PCBs, PAHs, petroleum hydrocarbons), inorganic (As, Cd, Cu, Cr, Hg, Ni, Pb and Zn) contaminants and sediments characteristics (e.g. grain size, metal-binding phases, nutrients) were measured in whole sediment. To build the matrix of traits, we made a bibliographical research at the level of the genus characteristic. The traits were coded by taking into account regional peculiarities of climate and the same ecozone. The relative influence of the chemical contamination and the environmental characteristics on the structure of the bioecological traits was estimated by multivariate analyses. The results of stations clustering according to the traits, significant indicators traits according to the clusters and the relations with the explanatory variables will presented.