Which of the following is recognised as the national aquatic (water) animal of India?

Introduction / Context:
India has adopted several national symbols to represent its natural heritage and cultural identity, such as a national flag, national animal, national bird and national aquatic animal. Knowing these symbols is a key part of static general knowledge. The national aquatic or water animal recognises the importance of conserving river ecosystems and endangered species in the country.

Given Data / Assumptions:
- The question asks specifically for the national aquatic or water animal of India.
- The options include Crocodile, Turtle, Alligator, Gangetic dolphin and River shark.
- No year is mentioned, so the standard and widely accepted designation is assumed.

Concept / Approach:
The Government of India declared the Ganges river dolphin, also called Gangetic dolphin, as the national aquatic animal to draw attention to the fragile condition of river ecosystems, especially the Ganga system. The concept behind the question is that the national aquatic animal is not a general marine creature like a shark but a specific endangered freshwater dolphin found in Indian rivers.

Step-by-Step Solution:
Step 1: Recall that India has designated the Ganges river dolphin as its national aquatic animal. Step 2: Match this information to the given options and identify which option describes that animal. Step 3: Crocodile, Turtle, Alligator and River shark are not the ones declared as national aquatic animal, although some may be found in Indian waters. Step 4: Recognise that Gangetic dolphin refers to the same species as the Ganges river dolphin. Step 5: Select Gangetic dolphin as the correct answer.

Verification / Alternative check:
Official announcements by the Government of India and material from the Ministry of Environment and Forests state that the Ganges river dolphin has been given the status of national aquatic animal. Exam oriented books and environmental awareness campaigns also highlight this fact. Seeing the term Gangetic dolphin used as an alternative name confirms that option D is correct.

Why Other Options Are Wrong:
Crocodile: Although crocodiles live in Indian rivers and lakes, they have not been declared the national aquatic animal.
Turtle: Certain turtles are protected species, but turtle is not the symbol chosen as national aquatic animal.
Alligator: Alligators are not native to Indian rivers in the same way as the Ganges river dolphin.
River shark: While some sharks may occur in rivers, this term does not refer to the national aquatic animal of India.

Common Pitfalls:
Students sometimes confuse the national animal (the Bengal tiger) and the national aquatic animal, or they associate crocodiles with rivers more strongly than dolphins. Another error is to think that a widely feared species such as a shark would be chosen as a national symbol, which is not the case here. Remembering that the government selected an endangered freshwater species reinforces the correct association with the Gangetic dolphin.

Final Answer:
The national aquatic or water animal of India is the Gangetic dolphin.