The question requires identifying a fruit crop specifically known for its 'very high level of fat'. We analyze the provided options based on this nutritional characteristic.
Different fruits have distinct nutritional profiles. While most fruits are primarily sources of carbohydrates and water, some contain significant amounts of fat.
Based on nutritional data, Avocado is distinctly characterized by a 'very high level of fat' compared to Mango, Grape, and Water apple. Therefore, Avocado is the correct identification.