To study the biomonitoring capacity of some seaweeds from the Nador lagoon “Marchica”, we have analyzed the physico-chemical parameters of lagoon water (3 sites) including temperature, dissolved oxygen (DO), pH, salinity, turbidity, NO₃^-, NO₂^-  and PO₄^2-, and also we determined some biochemical parameters such as chlorophyll, protein, glucose and proline concentrations of 4 seaweeds (Gracilaria gracilis, Alsidium corallinium and Ulva rigida and Caulerpa prolifera). Waters and algae samples were collected in July 2015, from three sampling sites (S1, S2 and S3). Variations in the physical and chemical parameters were observed between sampling stations. The site 2 was the most polluted area characterized by high levels of turbidity, NO₃^-, NO₂^- and PO₄^2-) followed by the site 1 with high NO₃^- and NO₂^- concentrations. In relation to biochemical parameters in different algal species, the Alsidium corallinium showed a higher level of chlorophyll a and b in sites 1 and 2 comparing to the site 3. Finally, Gracilaria gracilis collected from the site 2, accumulated more proteins, glucose and proline. From these results, we can conclude that algal species found in the Nador lagoon “Marchica” can be used in the biomonitoring of pollution in a marine ecosystem.