Main reason of water bloom in rivers, lakes, sea etc. is:

Options

A. Brown algae and green algae
B. Cyanobacteria and dinoflagellates
C. Eicchornia
D. Fishes

Answer

### Step-by-Step Solution:

1. **Understanding Water Blooms**: Water blooms refer to the rapid increase in the population of algae or other aquatic organisms in water bodies like rivers, lakes, and seas. This phenomenon can lead to significant ecological changes and can affect water quality.

2. **Identifying the Causes**: The main causes of water blooms are nutrient enrichment processes, particularly eutrophication. Eutrophication occurs when water bodies receive excess nutrients, primarily from agricultural runoff, industrial waste, or sewage discharge.

3. **Nutrient Sources**: The nutrients that contribute to eutrophication are often phosphates and nitrates. These nutrients promote the rapid growth of algae and other aquatic plants.

4. **Types of Organisms Involved**: The organisms primarily responsible for water blooms include:
- **Cyanobacteria**: Also known as blue-green algae, these microorganisms can grow rapidly in nutrient-rich waters.
- **Dinoflagellates**: These are another group of algae that can cause blooms, some of which are toxic and can lead to phenomena like red tides.

5. **Analyzing the Options**:
- **Option A: Brown and Green Algae**: While these can contribute to blooms, they are not the main culprits.
- **Option B: Cyanobacteria and Dinoflagellates**: This is the correct answer as both are known to cause significant water blooms, especially in nutrient-rich conditions.
- **Option C: Cornea**: This is not relevant to aquatic ecosystems.
- **Option D: Fishes**: Fish do not cause water blooms; they are affected by them.

6. **Conclusion**: The main reason for water blooms in rivers, lakes, and seas is the presence of cyanobacteria and dinoflagellates, which thrive in nutrient-rich environments.

### Final Answer:
The main reason for water blooms in rivers, lakes, and seas is **Option B: Cyanobacteria and Dinoflagellates**.

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