The injection of oxygen to a flotation basin in the process of removing pollutants from water streams comprising applying a flocculating or coagulating agent to a portion of the water stream, and creating a flocculation basin along the water stream. The injection of oxygen includes submitting the aggregate particles with higher dimension and density located upstream of the portion of the water stream to at least one of dissolving and injecting oxygen, directing same to dissolving plants through pressurized mixers, thus forming a water/oxygen mixture to be injected to portions of the water stream, causing the aggregate particles to float; creating a flotation basin along the portion of the water stream, the agglomerated material present upstream on the surface and by the banks of the water stream being removed by scraping the surface of the water stream.