The purpose of this study was to use total organic carbon (TOC) and dissolved organic carbon (DOC) in water and sediment samples to assess the water quality of Moro reservoir, Ilorin, Nigeria. The study was conducted from August 2015 to February, 2016. TOC and DOC have a major influence on both the chemical and biological processes that take place in surface sediment and water. TOC and DOC concentrations in water and sediment samples were determined using TOC-VCSH method with ASI-V auto analyzer. All surface waters samples from the reservoir were characterized by increased organic substances concentration levels. TOC and DOC in water and sediment had significant correlation with each other respectively. TOC and DOC concentrations in water samples were in the range of 0.159 to 11.7680 and 0.088 to 10.898 gCl-1, respectively, whereas TOC and DOC concentration in sediments varied between 3.78 to 43.9 and 2.56 to 30.22 gCKg^-1, respectively which was within range for pollution tolerant benthic macro-invertebrate. High organic carbon content of the reservoir was due to inputs of external organic carbon from run-off, internally produced organic carbon from aquatic organisms’ remains and the impoundment itself which allows for accumulation of carbon from the trapping of particles and alteration of flow regime. More than 80% of TOC in sediment samples from the reservoir were above threshold value >10 gCKg^-1 making profundal sediment azoic; this was due to contaminant associated with organic carbon concentrations and physiological stress factors. From the results it is concluded that the reservoir water is highly polluted and should be managed for human welfare and sustainable use for domestic water supply.

Keywords: Organic carbon, water quality, contaminants, profundal sediment, Moro reservoir.

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