In 2004,ammonia concentration in raw water of Sitalakhya River at the eastern periphery of Dhaka was found higher than the expected rate of 4 mg/Lforecasted in feasibility studies,with a value of about 8 mg/L, which could not be removed by conventional treatment chain employed at Dhaka, hence, recentlyan ammonia removal plant has been constructed. This important background has ledto the current study on ammonia, a single quality parameter to understand the trend of deterioration, its probable causes, and the probable remedy.Water samples have been collected and tested for ammonia for a period of fifteen years, from 2002 to 2017, mostly in the laboratory of the existing plant. Ammonia levels have been found generally below 4 mg NH4-N/L in the wet season,though during the dry season they rise up to 20 mg NH4-N/L (sometimes more). The maximum and average values of concentration follow a more or less similar pattern with time, withboth average and maximum values, increasing around 1 mg/L annually,suggesting a similar trend in future which will make the existing treatment process inadequate. This needs attention in terms of both regulatory measures and proactive strategies on how to handle the resulting future challenges.