They are usually grass-green in colour. Green algae are by far the most abundant algae. They out-number all other algae together. They reproduce by merely splitting in half.
Green algae give pond water a slightly green colour.
All green algae are microscopic but some forms organize themselves into visible colonies. Each cell of the colony has two flagella and an eyespot. The eyespot detects light and helps the colony stay in sunlight. The whole sphere rotates and rolls through the water. Sometimes the sheets or looser nets curl into cylinder shapes.