How do chemicals (nitrates, phosphates and chlorine) get into the water of lakes and rivers?

One cause of nitrates and phosphates in lakes and rivers is from fertilisers. Farmers fertilise their crops, and rainfall washed this into the rivers, polluting them. Chlorine, in salt can get into lakes and rivers due to salinity in the soil. If land is cleared, the rising water table can cause salt to come to the surface, which is in turn washed into rivers and lake.