**Abstract**

The lake of Xochimilco, Mexico presents a high degree of chemical contamination, despite belonging to a Protected Natural Area and RAMSAR site, due to this, it was decided to evaluate the quality of its waters and propose solutions to its contamination. The objective of this work was to know the relationship that exists between the microalgae species associated with a dump that affects the site, coming from a Wastewater Treatment Plant and the physicochemical factors coupled with the development of bioassays. Water sampling was carried out in the site and adjacent areas to know the microalgae species and their cleaning role, in addition to laboratory bioassays to verify the results. There are 88 species of microalgae and their influence on water cleaning. In laboratory, it was confirmed that some algae species were purifiers of contamination by nutrients.

**Keywords:** residual water treatment, microalgae, physicochemical factors, Xochimilco, Mexico
