Coastal sediments are a powerful tool for analyzing pollution levels and reconstructing history. The Oualidia lagoon plays an essential role in the local economy as it provides several ecosystem services, including aquaculture, fisheries, and coastal tourism, among others. Therefore, the conservation and protection of this natural system requires the continuous monitoring of its environmental quality. In light of this, the present study evaluates the potential ecological risk of Cr, Cd, Pb, and As accumulation in coastal sediment cores collected from the Oualidia lagoon. These sediment cores were also dated using lead-210 in order to study the temporal variations of the studied metals. The ecological risk values of the metals show that among the four metals, cadmium indicates a very high ecological risk in the first 25 cm and 15 cm of sediment cores (CO-1 and CO-2, respectively). The high potential ecological risk of the sediments recorded in the surface layers suggests that the development of human activities in the last two decades has contributed to the increase of heavy metal concentrations. Activities such as agriculture can be potential sources of Cd. Excessive use of fertilizers and pesticides may have contributed to the increase of this heavy metal in the lagoon. This finding highlights the need for careful monitoring and remediation of Cd levels in this aquatic system, as it presents a high ecological risk value among the selected heavy metals.