Citarum River is the largest natural stream in West Java, Indonesia, flowing across an area of 6614 km(2). About 3000 industries discharge their wastewater into the stream, affecting almost 19 million people who live along the river. Considering the perseverance and the prospective toxicity of microplastics (MPs), investigating their concentrations in this river is critical to help illustrate the exposure of the risks to the residents of the area and beyond. This study was focused on identifying the MPs concentrations in the water, sediment, and milkfish (Chanos chanos). A volume-reduce method by using manta trawl was used to take water samples. Sediment and milkfish samples were taken using a grab sampling method. Digestion of fish was using Fenton oxidation method according to weighted ratio (1:5) and H2O2 30% (w/v). The average MPs concentration in the river was 0.0574 +/- 0.025 particles/m(3); in the seawater ponds 3.000 +/- 2.645 particles/L; and in the mixed-water ponds, where the water from the river and the sea were mixed, 0.666 +/- 0.577 particles/L. The average MPs concentration in the sediment of Citarum River was 16.666 +/- 0.577 particles/100 g; in the seawater ponds 13.335 +/- 1.527 particles/100 g; in the mixed-water ponds 11.665 +/- 0.577 particles/100 g; and in the seawater 3.335 +/- 0.331 particles/100 g. The average of MPs concentration in the gut and gills of milkfish in the seawater ponds was 2.666 +/- 2.333 particles/fish, and in the mixed-water ponds was 1.166 +/- 0.983 particles/fish. The average of MPs concentration in the milkfish tissues taken from the sea was 1.333 +/- 0.577 particles/fish; and for the ones taken from the mixed-water ponds, the concentration was 1.111 +/- 0.838 particles/fish. Using the Kruskal Wallis test to generate statistical analysis, there is a significant difference between the MPs concentrations in the water and sediment samples of Citarum River based on their locations (p value=0.024 and 0.032<0.05). The most dominant plastic polymers in the samples were polyethylene (PE) and polypropylene (PP). There is no correlation between the level of MPs concentrations in water and sediments and the level of MPs concentrations in milkfish. However, the existence of microplastics in every sample that came from different points in the sampling area should sound an alarm, either to the local government or residents.