Concept lattices are useful tools for organising and querying data. In this paper we present an application of lattices for analysing and classifying stream sites described by physical, physico-chemical and biological parameters. Lattices are first used for building a hierarchy of site profiles which are annotated by hydro-ecologists. This hierarchy can then be queried to classify and assess new sites. The whole approach relies on an information system storing data about Alsatian stream sites and their parameters. A specific interface has been designed to manipulate the lattices and an incremental algorithm has been implemented to perform the query operations.