What is the primary environment where didymo is found?

Didymo, also known as "rock snot," is primarily found in freshwater rivers. This algae thrives in cold, nutrient-poor waters and is often associated with high flow velocity and specific substrates like rocky riverbeds. Freshwater environments provide the optimal conditions for didymo to bloom, which can lead to significant ecological impacts, such as altering habitat for aquatic organisms and affecting water quality.

The other environments listed, such as saltwater oceans, brackish estuaries, and wetlands, do not provide the conditions suitable for didymo growth. Saltwater environments have different salinity that does not support this freshwater algae, while brackish estuaries, which feature a mix of salt and fresh water, also do not create the ideal habitat for didymo. Wetlands can have varying salinity and water conditions that may not be consistent with the requirements of didymo, making freshwater rivers the predominant habitat for this organism.