Addressing bioassessment of tropical rivers using macrophytes: The case of Itanhaém Basin, São Paulo, Brazil

•A 5-step approach to derive a bioassessment tool in tropical rivers is proposed.•An aquatic plant-based index for monitoring tropical coastal rivers in Brazil was developed.•Life-forms and diversity measures provided a metric pool for the index construction.•The index (MIBI-ITA) detects high nitrogen and phosphorus contents in water and sediments.•Further research on plant traits and dynamics of change is needed to improve MIBI-ITA.