Find out what do the terms 'algal bloom' and 'red tides' signify.

Explanation

### Step-by-Step Solution:

1. **Understanding Algal Bloom**:
- Algal bloom refers to the rapid and excessive growth of algae, particularly blue-green algae, in water bodies.
- This phenomenon is primarily caused by the enrichment of nutrients, especially nitrogen and phosphorus, in the water.

2. **Causes of Algal Bloom**:
- Nutrient enrichment occurs due to various factors such as agricultural runoff, sewage discharge, and other human activities that introduce excess nutrients into aquatic systems.
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