Assessing Limnological Characteristics and Water Quality Index of the Rivers of？Northern Bangladesh

Different water quality indices (WQI) were determined to assess the limnological characteristics from five rivers of Dinajpur Bangladesh for fish production, agricultural uses, household and industrial purposes.Water quality index reveals large seasonal variation of two major seasons and indicates that the river water is suitable or unsuitable for drinking and other household uses.In the selected areas, temperatures in all warm-water fishes were within normal limits (20C -32C) and the waters were slightly acidic to neutral in characters, excellent for fish production (pH fluctuated from 6.8 -7.5 during the dry season and 5.8 -6.6 during the monsoon season).The dissolved oxygen (DO) value for fish production was above the safe limits (5 mgO2/L).The COD (chemical oxygen demand) of the river waters was within the satisfactory levels for fish production (4 mgO2/L by CODMn).The most frequent cations were Ca 2+ , Mg 2+ , and Na + , while 3 HCO -and Cl -were the most dominant anions.The principal cation and anion ratios in the water samples indicate that calcium and magnesium-containing minerals predominate over sodium-containing minerals.According to the Canadian Council of Ministers of the Environment's water quality index, the overall quality of the river waters is in the 'marginal' category.The concentrations of Cu 2+ , Zn 2+ , Mn 2+ and Fe 3+ were within the 'safe' limit for algae production.Ammonia levels in both seasons were within the acceptable limits for fish production.However, continuous monitoring is required to follow changes in river water quality through time and space.