The alga found in still fresh water is

Options

A. Sargassum
B. Laminaria
C. Polysiphonia
D. Spirogyra.

Answer

To determine the alga found in still freshwater, we can analyze the options provided:

1. **Sargassum**: This is a type of brown alga. All brown algae are primarily marine organisms, which means they are not typically found in freshwater environments. Therefore, we can eliminate this option.

2. **Laminaria**: Similar to Sargassum, Laminaria is also a brown alga and is found in marine habitats. Thus, this option can also be ruled out.

3. **Polysiphonia**: This is a red alga that is predominantly marine. While there are some freshwater species of red algae, Polysiphonia itself is not one of them. Hence, we can eliminate this option as well.

4. **Spirogyra**: This alga belongs to the green algae group, which is known for being found in freshwater environments. Therefore, Spirogyra is the correct answer as it is commonly found in still freshwater.

In conclusion, the alga found in still freshwater is **Spirogyra**.