This publication assessed the water quality and ecological aspects of the Ouro Creek, in the municipality of Caxias/MA, by analysing physical, chemical and biological parameters, with a view to determining its classification and suitability for its various uses. The quality and alterations to the water body were analysed using physical parameters (pH, Conductivity, True Colour, Turbidity, Temperature, Total Solids and Total Dissolved Solids), chemical parameters (Nitrite, Nitrate, Total Phosphorus, Alkalinity, Iron, Total Hardness and Ammoniacal Nitrogen) and biological parameters (Macroinvertebrate indicators). Finally, it compared the hydrological quality of the Ouro stream with CONAMA Resolution 357 of 17 March 2005 for surface waters. The assessment of the physical-chemical parameters of the water quality of the Ouro Creek served to alert the public authorities to take decisions with a view to conservation campaigns aimed at Caxiense society, especially the communities that are in its surroundings, with a view to using it sustainably in order to protect biodiversity and the biological balance of aquatic organisms.