Small urban rivers are thought to be major sources of riverine litter, especially macroplastics, into the ocean. In well-developed countries, waste management infrastructures and recovery systems are sometimes implemented to prevent their emission into the sea meeting environmental and economic goals. The Huveaune River in Marseille, South of France, is a typical case study showing a non-negligible and uncontrolled leakage of riverine litter remains, despite all recovery systems implemented. Giant bar screens are settled over the river to collect riverine litter from the whole water column before water is released into the Sea. In this paper, screened material was characterized during a dry, wet and heavy rainfall period and annual macroplastic mass flows were estimated. The plastic fraction represented 83% by count of the 3147 items sorted and counted. Mass flow of plastic debris ranged between 1.1 and 5.8 mt/yr (equivalent to 2.1–11.4 g/cap/yr), in which 0.4–2.1 mt/yr (equivalent to 0.8–4.1 g/cap/yr) are bypassed to the sea during heavy rainfall periods. Giant bar screens across the Huveaune River prevent 65% of the mass flow to reach the sea annually, but 35% remain uncontrolled. When compared to the Seine River and other European Rivers, macroplastic leakage into the ocean per capita may range between 1 and 10 g/cap/yr. This suggests that end-of-pipe solutions are not enough and further supports urgent regulations of the plastic production on local to global scales to tackle the plastic pollution at its source.