Fertilizers and animal manure, which are both rich in nitrogen and
phosphorus, are the primary sources of nutrient pollution from
agricultural sources. Excess nutrients can impact water quality when it
rains or when water and soil containing nitrogen and phosphorus wash
into nearby waters or leach into ground waters. This results in high rate algae bloom interfering with aquatic life.
On the other hand some materials like withered plants contains no chemical substances harmful to the acquatic life and even if large amount if it is released in the water bodies no great negative effect will be noted.