ENGLISH
REFERENCE

algae

n.
US //ˈæɫdʒi// UK //ˈælɡiː// al·gae
  1. 1 aquatic organisms (n.)
    B2 Upper Intermediate Technical Science

    simple organisms that grow in water and use sunlight to make food, like seaweed or pond scum.

    photosynthetic, eukaryotic organisms that lack true roots, stems, and leaves; the term is often used collectively for the green or brown mass found in water.

    Example

    The pond was covered in a thick layer of green algae after the hot summer.

    Example

    Excessive nutrient runoff from nearby farms led to a massive bloom of toxic algae, depleting oxygen levels in the lake and killing the fish population.
    Pitfall
    The algae is growing fast.
    The algae are growing fast.

    In scientific and formal writing, 'algae' is the plural of 'alga' and takes a plural verb.

Last updated June 20, 2026