The decomposition of organic matter is a key process in the functioning of rivers. This organic matter is an important source of energy and nutrients in food webs. The objective of this work is to evaluate the degradation of the litter of three plant species in the water of the Okpara River. The degradation of the three leaves (Piliostigma thonningii, Terminalia avicennioides and Flueggea virosa) was made during the rainy season by using the litterbag technique of different mesh sizes which are large mesh (LM) of 5 mm and fine mesh (FM) of 0.5 mm. A total of 96 litterbags, each containing 3.5 g of dried litter were used; 32 litterbags (16 LM litterbags and 16 FM litterbags) per species. These litterbags were placed in the Okpara River waters during 28 days and 24 litterbags are recovered at four different dates: one week, two weeks, three weeks and four weeks. At each recovery date, four (04) physicochemical parameters (temperature, pH, conductivity and TDS) were measured and the macroinvertebrates were harvested. The study found that Fluggea leaves decompose and lose their weight faster than those of Terminalia and Piliostigma, a very rapid loss since it reaches the value of 58.29% of the initial weight in 28 days only. This loss of initial weight could be related to the structure of the leaf, the action of microorganism and the moderate rise in temperature (26 °C) favoring a biological activation. The study also revealed the dominance of the Chironomidae family and functional collector groups.