1. Phosphate and nitrate are …………………………..that can be washed into rivers and they are nutrient resources of algae. A great number of bacteria takes up all oxygen in the water to decompose the dead algae, the lack of oxygen lead to the death of other marine and fresh water lives, the process is known as ………………………………..
2. The …………………………… of agricultural wastes into water sources can be harmful when the level of ……………………………….. is high enough.
3. With excessive use of fertilizers around the river banks, the amount of dangerous chemicals in water can be dramatically …………………………………
4. Different kinds of …………………………………… that have been ……………………………. in the rivers can transferred to human via the consumption of fish from polluted water.