For the first time, the proliferation of yellow mucus algae was found in the Orcopampa, Caquemayo and Pillones rivers in the province of Arequipa, Peru. The causative agent corresponds to Gomphoneis minuta of the blooms, confirming it by scanning electron microscopy; diatomea with biseriate striae, raphe along the valvar face and muscilaginous peduncles at its basal end, being considered the first record for this area. It is necessary to implement monitoring programs to control and prevent their spread. In addition, the fact that G. minuta has been found in considerable extent in the Orcopampa, Caquemayo and Pillones rivers makes us presume that it would be capable of transforming into a taxon potentially harmful to the aquatic ecosystem and, similarly to D. geminata, it would need monitoring and surveillance programs to prevent its spread.