It important to aquatic system of offspring of crustacean and the molluscs such as snails and slugs as they form protected and conducive areas for their lives
It meet at point called estuaries where fresh water meet salt water is result is diluted salt water which may appears blackish
Most likely because you don't know what could be in tap water (chemicals, germs)
Atmosphere
biosphere
hydrosphere
the main oxygen cycle is photosenthisis
