This study examines time and trend plots: Application to aggregate mean of water pollutants discharged in streams and rivers in Ibadan environs. The data was collected from the Ministry of Environment and Water Resources, Secretariat, Ibadan, Nigeria. This study is therefore meant to study the impact of the regulatory measures by the government on the discharge of water pollutants in streams and rivers. It is supposed that with these regulatory measures, water pollutants discharge in streams and rivers should be on the decrease. Specifically, data were collected on alkalinity; total hardness; calcium hardness; magnesium hardness; total solids; total suspended solids; total dissolved solids; chloride; sodium chloride; dissolved oxygen; biochemical oxygen demand; chemical oxygen demand; oil and grease. The study reveals (1) Aggregate mean of water pollutants quarterly. (2) Gradual reduction of water pollutants discharge in streams and rivers from the fitted model (3) Gradual increase of water pollutants discharge in streams and rivers from the predicted values.