The agricultural and industrial activities that are developed to the riverbanks of the river Catatumbo from Colombia made the Venezuelan territory, they are altering the quality of the waters of the river Catatumbo, being necessary their characterization. The phosphorus concentrations and nitrogen were evaluated in samples of water in the low part of the river Catatumbo, in 10 stations: 4 in the ... [Show full abstract] river Catatumbo, 5 lagoons and 1 station in the Lake of Maracaibo (in front of the outlet of the river Catatumbo). The concentration average, of total nitrogen and phosphorus respectively, in stations of the river Catatumbo was of 1,05 mg/L and 0,31 mg/L, in the lagoons of 0,87 mg/L and 0,12 mg/L; and in the lake of 0,67 mg/L and 0,18 mg/L. The nitrogen concentration in water is bigger than the certain one for phosphorus, being presented the nitrogen in smaller form as inorganic nitrogen and the match like dissolved phosphorus. In the lagoons the phosphorus concentrations went smaller to those reported for the stations located in the river. The results indicate that the transport of materials laughs below coming from the high areas; it is possibly retained in the plane areas and lagoons of Juan Manuel's marsh. It is necessary the necessity to increase the protection and recovery of the different forest that surround the river Catatumbo, as well as of regulating the activities that are carried out in both countries, to counteract the haulage of nutritious to the same one and possibly to the Lake of Maracaibo. © 2011 2002 Revista Técnica. Facultad de Ingeniería. Universidad del Zulia.