<p>The omnipresence of microplastic (MP) particles in environmental matrices of rivers is on the rise and has become a focal point of aquatic research. The study investigated the spatiotemporal distribution of MPs and adsorption of heavy metals (HMs) in the Buffalo River of South Africa. The findings of the study showed that a sum of 874 MPs was enumerated from the samples collected in the river system. The MP particles ranged between 0.35–0.75 particles·L⁻¹ during the dry winter and 0.3–0.9 particles·L⁻¹ in wet summer seasons in surface water. The range in sediments was 3–32 particles·kg⁻¹ and 2–23 particles·kg⁻¹ during the dry winter and wet summer seasons, respectively. The results showed that temporal rainfall patterns had a significant (<i>p</i> = 0.009 &lt; 0.05) influence on MP abundances in sediments. Fibers and fragments were the main shapes, while polyethylene and polypropylene were ubiquitous. HMs such as nickel, copper, and iron with concentrations of 36.49 ± 3.96, 14.33 ± 0.87, and 356.47 ± 73.66&#xa0;µg·g⁻¹ were adsorbed on surfaces of the microplastics, with iron being strongly correlated with the 3&#xa0;mm and 1&#xa0;mm size fractions and copper with the 2&#xa0;mm fraction. The study has provided insights into the influence of climatic conditions on MP abundances and how plastics adsorb chemical pollutants such as HMs in environmental conditions. Moreover, the study has yielded baseline data on MP pollution in Buffalo River, which is helpful to the relevant authorities of the country’s ongoing River Health Program.</p>