This research explores physico-chemical characteristics and fish abundance and diversity of Mairua Reservoir Water, Funtua, Katsina State, North-Western Nigeria. The duration of the study was 12 months starting from September to August, 2017, using standard methods and procedures.The result revealed that; Water temperature (25.02 ± 0.170C) pH (7.54 ± 0.03), Alkalinity (3.69±0.09), Conductivity (129.43 ± 5.15μЅ/cm), Total Dissolved Solids (50.54 ± 0.57mg/L) Nitrate-nitrogen (0.21 ± 0.04mg/L), Water Hardness (134.44 ± 3.06mg/LCaCO3), Dissolved Oxygen (3.98 ± 0.10mg/L),Biochemical Oxygen Demand (2.53 ± 0.08mg/L), Phosphate-phosphorus (0.19 ± 0.02mg/L),Chloride (5.09 ± 0.15mg/L),Sulphur-sulphate (0.21± 0.01) and Calcium (2.97±0.06mg/L) respectively were  all varied with months and seasons. Analysis of variance indicated significant difference between seasons (P < 0.05).Out of the total number of fish species (8273) identified; the result indicated Fish fauna percentage composition were Coptodon zillii: 1980 (23.9%), Clarias gariepinus: 1560 (18.9%), Oreochromis niloticus: 1020 (12.3%), Lates niloticus: 860 (10.4%), Bagrus. Bayad: 632 (7.6 %), Mormyrus senegalensis: 973 (11.8%), Labeo senegalensis: 595 (7.2%) and Synodontis clarias: 650 (7.9%). Results also indicates most of fish species were positively correlated with the water quality parameters in all the sites studied. Hence, there were fish abundance and a sustainable livelihood amongst the fishermen. However, a careful management strategy and routine monitoring from both government and non-governmental organizations are critical for the improvement and sustenance of the fisheries resources of the reservoir.