The management of the swamps must consider environmental aspects. The construction and operation of swamps suppose an alteration of the sections of river that are waters down. With the present project, made by Limnos S.A. in 1996, for the Hydrographic Confederation of the Ebro, it was tried to compile the problematic information related to the environmental problem of the swamps. The project has included the diagnosis of 38 swamps and the fluvial sections located waters down, the definition of its environmental risks, a proposal of measures, and simple procedures of pursuit and control