Abstract: Background: The parasite Anguillicoloide scrassus causes profound damage to the swim bladder of eels and may impair their spawning migration to the Sargasso Sea to complete its reproductive cycle. In this investigation, evaluated the current infection rate (by lumen worms of the swim bladders) and past infections (e.g., as evidenced by damage to the swim bladders) of the European eels that populates three water dam of Parc National of El Kala (Northern Africa). Materials and Methods: A seasonal rate was performed, by collecting parasites and measuring morphological parameters (length and weight of fish) from the three water dam: Tonga lake (96 eels of length ranged from 359 and 630 mm), Oubeira lake (135 eels of length ranged from 412 and 650 mm) and Mellah lagoon (147 eels of length ranged from 261 and 825 mm) of the Parc National of El Kala. After dissection, the classical epidemiological parameters and the SDI were calculated. For analysis of data STATISTICA 8.0 Software was used. Results: The results revealed a mean prevalence of 29, 67.16 and 4.26%, a mean intensity of infestation of 2.8, 7.46 and 2.89 per swim bladder, a mean abundance of 0.86, 4.94 and 0.21 per eel in Tonga, Oubeira and Mellah, respectively. The highest prevalence values are recorded in larger fish and all eels of the sampling area show pathological signs of infection in their swim bladder, however, it is the eels of the lagoon that are the least affected. Conclusion: The evaluation of the swim bladder degenerative index (SDI) remains an important tool to estimate the health state of the swim bladder and represent a meaningful measure in epidemiological studies of anguillicolosis.