The study was conducted in the Salinas Grandes estuary, department of León, from June to November 2017. The aim consisted in evaluating the fluctuations of the main groups of microalgae and relating them to the fluctuation of the physicochemical parameters. The water sample was taken once a month, the physical-chemical parameters were measured (salinity, oxygen, temperature, pH and turbidity). In general, our results show the presence of three of the four groups (Diatoms, Chlorophytes and Dinoflagellates) being Diatoms and Chlorophytes the groups that presented higher concentrations. With respect to salinity, the month of July has the highest concentration with (35 ppm) decreasing over time in the whole area. The dissolved oxygen ranged between 5.9-1.8mg / L in the entire study period. The maximum temperature values were presented in the month of August (30.5 ° C), without significant changes in time and between sampling points. With regard to turbidity, readings ranged between 43-180 cm, with June being the month with the lowest readings. Throughout the study period, the pH value of the water presented a range of 7.06-8.56. Diatoms and dinoflagellates showed a positive correlation in Guasimo and La Flor. Likewise, no positive correlation was observed between dissolved oxygen levels and turbidity. Guasimo presented the best values of dissolved oxygen during the study period. However, its are not optimal for animal welfare.