Water quality of Kaptai reservoir in Chittagong Hill Tracts of Bangladesh

A study was conducted in Kaptai reservoir, one of the largest man-made freshwater lakes of South-east Asia, to determine present status of water quality and its suitability for fishing and other uses. Water samplings were from middle part of the reservoir at 0.2 and 0.8 fractional depths at five different locations from upstream to downstream viz. Burburichara, Maichchari, Subolong, Basanthakum, and Rangamati. Water analyses show that concentrations of NO₃-N, K⁺ and total P, and suspended solid at all the sampling stations were beyond the recommended values for fish culture. Concentrations of Na⁺, Ca²⁺, Mg²⁺, SO₄ ²⁻, Cl⁻, total dissolved solid (TDS), dissolved oxygen (DO) and chemical oxygen demand (COD) were within the standards for aquaculture. Concentrations of NO₃-N, SO₄ ²⁻, K⁺ and total P showed no definite trend with depths, locations as well as rainy and dry seasons. Water pH, conductivity, Na⁺ and HCO₃ ⁻ contents were lower in rainy season, and DO and COD higher at almost all the locations in both the depths, compared with dry season. Total solids and concentrations of TDS, DO, COD, Ca²⁺, Mg²⁺ and Na⁺ were higher in upstream and decreased gradually towards downstream in the reservoir. Concentrations of DO and Ca²⁺ and pH were higher and Mg²⁺ less at 0.2-fractional depth than those at 0.8-fractional depth at almost all the locations. The reservoir is in mesotrophic condition containing high concentration of NO₃-N and total P, in alarming status with the presence of excessive suspended solids from urban pollution around the town. It is necessary to adopt measures for protecting water quality in the reservoir due to such deteriorations.