"In this work we aimed to determine if different sources of anthropogenic impact of different water bodies may affect the nitrogen (N) and phosphorus (P) contents of macroalgae biomass. To this end, samples of water and macroalgae were collected every second month in Urías lagoon (UR) and in Altata-Ensenada del Pabellón (AL and EP) lagoonal system of NW Mexico. The order of concentrations of dissolved N was UR> EP>AL (P<0.001), that of reactive P was EP>UR>AL (P < 0.001). The N content of the macroalgal biomass of the three lagoons was not significantly different, but the P content was significantly (P <0.001) lower in UR than in EP and AL. The N: P ratios in algal biomass seemed to indicate that N was below optimum values for growth in AL and EP, while P was below optimum in UR. However, the algae N and P contents were consistently high in the three lagoons, indicating adequate concentrations of external nutrients for optimum growth."