Estuaries are important for juvenile fish because they provide a unique and nutrient-rich environment that supports the growth and development of young fish. The mixing of freshwater from rivers and saltwater from the ocean in estuaries creates a diverse habitat with abundant food sources and protection from predators. Additionally, estuaries serve as transition zones where juvenile fish can adapt to changes in salinity, temperature, and water quality before moving into the open ocean. These factors make estuaries critical for the survival and well-being of juvenile fish populations.