The effects of various environmental factors, sedimentation and attachment of faecal coliforms on water hyacinths, Eichhornia crassipes, were investigated in a pilot-scale water hyacinths pond. This investigation was conducted to evaluate the role of solar intensity, pH, dissolved oxygen, temperature, sedimentation, and attachment of faecal bacteria on Eichhornia crassipes on disappearance of bacteria in a water hyacinths pond. A mathematical model that used the plug flow philosophy and incorporated aforementioned factors to predict faecal coliform mortality rate was developed. The proposed multifactor model satisfactorily predicted mortality rate of faecal coliforms in a pilot-scale water hyacinths constructed wetland. The environmental factors such as solar intensity and pH were the key factors if the coverage of water hyacinths is minimum, but attachment of bacteria to water hyacinths played a major role in a wetland fully covered with water hyacinths.