The Biological Diatom Index (BDI) is a regulatory indicator used for the assessment of the biological quality of French water bodies within the Water Framework Directive. In particular, this index considers the proportion of deformed diatoms, whose presence probability profile is an indicator of stress. Although this is a sensitive criterion, it is rarely informed as there is no consensual objective approach for attributing a teratological character to a diatom when the deformation is subtle. In this context, our project aims at documenting the most common teratologies by developing an iconographic collection of deformed diatoms on the French territory. This tool, which will be designed and fed by surveillance operators, will provide them assistance in determining the teratological status. For this purpose, a collaborative web interface will be implemented in order to acquire a large database of teratology images, illustrating the specific diversity, or on the contrary the stability, of the types of deformations encountered for French mainland diatom species. On the long term, sharing knowledge on the deformations observed on the territory and associated environmental conditions will be key to guarantee the quality of the existing BDI, by optimizing the use of diatom deformation for the assessment of toxic stress. This poster will illustrate the first steps of this crowdsourcing approach.