Farmers consider pesticides and fertilizers necessary to ensure successful farming. what problems are caused by the use if these agricultural pollutants?
the increased nitrates from the fertilizers leech into the water and cause algal blooms, which take oxygen out of the water and this suffocates fish.
pesticides seem to pose no environmental problems.
the increase greenhouse gases.

The answer is The increased nitrates from the fertilizers leech into the water and cause algal blooms, which take oxygen out of the water and this suffocates fish.. 

Algae blooms are the consequence of large amounts of farm fertilizers in the rivers, which increases nitrates level in the water. Algae use the presence of increased nutrients and enhance their own growth. It is known that they produce an oxygen in the photosynthesis, so it is not a problem while they are still alive. But when these organisms die, their decomposition begins. For the process of decomposition, the oxygen is needed and ultimately it will be depleted from a body of water. This could lead to the death of aquatic animals, such as fish, that depend on oxygen.

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