Final answer:
The main cause of eutrophication in bodies of water is fertilizer runoff, which leads to excessive plant growth and water quality deterioration.
Step-by-step explanation:
The main cause of eutrophication in bodies of water is fertilizer runoff. When excess fertilizers from agricultural activities or home gardens are washed into water bodies, they provide an abundance of nutrients like nitrogen and phosphorus. These nutrients promote the rapid growth of algae and other aquatic plants, leading to excessive plant growth, oxygen depletion, and the deterioration of water quality.
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