The main fertilizer used in agriculture, including compounds of nitrogen and phosphorus Phosphorus in the form of phosphate can be attached to the soil. It is less that flows with the water. So the substance problem is nitrogen. Fertilizer use most often put together more than plants are used. When it rains, rain will wash out the nitrogen flow through the ground into the river. Help the algae grow well, a lot of, rising tide of color, aroma, and when these algae you break down. It will make the operas stinks and phenol higher. The ceiling white floating on the surface.