"KLANG River is once again being polluted by sand$-$washing activities, and the dumping of silt and waste in Jalan Taman Seri Sentosa, off Jalan Kelang Lama in Kuala Lumpur. The area has been hoarded up$,$ and a notice board identifies it as a construction site for an apartment project. During a recent visit to the site, StarMetro witnessed dozens of $10-$tonne tipper lorries unloading sand to be washed. The trucks transport earth from other areas in the Klang Valley to be unloaded here. A suction pump can be seen at the area where water from Klang River is used to wash the sand. After the sand is washed, the wastewater, consisting of mud and silt, is dumped into the river. Sand$-$washing activities polluting Klang River $($The Star, June $9,2014)$ Based on the above case study, answer the followings: Predict possible pollutants in the discharge, and what is the effect to the water quality of the river.

If you have an authority, suggest ways to prevent or reduce the incidences from recurring.