Algae and seaweed are photosynthetic organisms that grow in a variety of aquatic environments, including marine and freshwater environments.
A big algae that grows in the sea or on rocks below the high water mark is known as seaweed.
Algae is a basic, non-flowering, and often aquatic plant of a large group, whereas seaweed is a large algae that grows in the sea or on rocks below the high water line.