How does the addition of pesticides and chemicals into lakes and streams affect an ecosystem?

The addition of pesticides and chemicals into the water of lakes and streams affects an ecosystem because it kills or weakens much of the fish population. Weakened fish are easy prey for predators, and predators that rely on fish for their food may find an insufficient supply. Another problem is that the water bugs or plant life that the fish feed on will increase in population, throwing off the balance of the ecosystem. Finally, algae and bacteria grow too quickly with the addition of chemical fertilizers.  This can cause dead zones, where there is not enough oxygen in the water for fish to survive.

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