This study was conducted to investigate the status of water quality for fisheries and aquatic environment in Chalan Beel, the largest wetland ecosystem in Bangladesh. Water samples were collected from five sampling stations over the period from February 2020 to January 2021 during the pre-monsoon, monsoon, and post-monsoon seasons, respectively. Surface water controlling parameters such as temperature, transparency, pH, DO, TDS, EC, total hardness, total alkalinity, Chlorophyll a, and TSI of Chalan Beel were monitored seasonally. The study revealed that temperature, transparency, pH, DO, TDS, EC, total alkalinity, total hardness, PO4, and NO3 exceeded the recommended level for fish culture. On the other hand, NH3, SO4, NO2, Chlorophyll a, and trophic state index (TSI) were within the standard limits for aquaculture. Concentrations of Chlorophyll a and TSI (CHL) indicated no definite trend with seasons. In conclusion, the wetland is in mesotrophic condition as the TSI (CHL) was within 40, and apparently, there was a positive relationship between Chlorophyll a and TSI. To conserve a healthy environment of the beel ecosystem, it is necessary to promote knowledge about water quality issues and beel management through monitoring and research.