This study evaluated the effects of the proximity of a domestic discharge on the biometric characteristics of the harpacticoid copepod Euterpina acutifrons in the Oum Er Rbia estuary (Atlantic coast, Morocco). Using comparative sampling between two locations - one near the discharge, potentially facing high pollution levels, and a less affected one - we measured six biometric traits of adult males and females under a light microscope. The Mann-Whitney test was utilized to analyze biometric variations. The results showed that at the discharge location (station S1), female total lengths ranged from 531.60 to 675.16μm (average 585.87± 54.70), and male lengths ranged from 451.20 to 578.94μm (average 502.45± 52.64). In contrast, at station S2, further from the discharge, female lengths varied from 553.46 to 634.46μm (average 596.78± 29.79), and male lengths varied from 472.97 to 641.54μm (average 578.83± 71.57). These measurements indicated a significant reduction in all mean biometric values, except head width, in males close to the discharge. No significant variations were found in females. A stronger positive correlation between biometric parameters was observed in males than in females. These findings are crucial for estuary conservation and management, highlighting the importance of monitoring pollution's effects on planktonic populations.