A new multimetric index for the evaluation of water ecological quality of French Guiana streams based on benthic diatoms

•As a French overseas department, French Guianas must meet the WFD requirements.•The previous diatom-based index was not appropriate for French Guiana streams.•The acquisition of 9 years of data allowed the development of a new local index.•The “alert taxa” concept was used to build a multi-metric index.•This new index will allow more relevant ecological status evaluation and/or diagnosis.