The areas on the margins of rivers, due to their hydrological, geological and ecological characteristics, need to be properly demarcated to be monitored and protected against human actions. In this context, the Protection Marginal Strips are of great importance and, thus, discussions about the norms that aim to protect these areas in urban environment become relevant, as many cities appear and grow along water courses without observing the land use and occupation regimes. In the State of Rio de Janeiro, the Instituto Estadual do Ambiente (INEA) uses to demarcate the Protection Marginal Strips of river minimum limits determined by State Decree 42.356/2010 that admits, for consolidated urban areas, lower limits than those established by the Brazilian Forest Code. The Piabanha River, that has its source in the Serra do Mar, in the municipality of Petrópolis, and flows into the municipality of Três Rios, was chosen as the object of work due to its importance as a tributary of the Paraíba do Sul River, one of the main sources of Rio de Janeiro. In addition, it has a large part of its extension in the mountainous region of the state, where flood events are frequent. Therefore, the technical-scientific approach of this work seeks to verify occurrences of removal of natural protection by deforestation and anthropic occupations in areas that have been excluded to Protection Marginal Strips of the Piabanha/RJ river, in consolidated urban areas, after the edition of the State Decree 42.356/2010, when it started to be applied in the demarcation of Protection Marginal Strips of waterbodies in the State of Rio de Janeiro.