Haematococcus lacustris is an extremely common, volvococcal alga. It is found in small and very small bodies of water, such as rock puddles, cattle troughs or bird baths, which can dry out regularly and are exposed to intense sunlight in summer. The algae can therefore cope with the most extreme conditions. When the water points dry out, the cells encyst and form red-orange coatings.

The most striking feature of Haematococcus lacustris is the large, spherical envelope with a distinct membrane in the middle of which the cell is located. It is attached to cytoplasm filaments, which are connected to the outer membrane. These cytoplasm filaments are often dichotomously branched at the distal end. Apically, the cell has a nose-shaped projection from which the two flagella extend. They are guided outwards through the sphere by two hollow tubes. The cell is thus completely shielded from the environment by this construction. Another characteristic feature is the large amount of orange-red haematochrome granules (a mixture of carotinoids) that accumulate around the central nucleus. One can assume a function as UV protection.

Many small contractile vacuoles are distributed over the entire cell. The cell has a cup-shaped chloroplast with several pyrenoids (usually more than 4). This distinguishes Haematococcus lacustris from the similar species Haematococcus droebakensis and Haematococcus Bütschlii, which have only two pyrenoids.

Haematococcus lacustris is one of the few industrially utilized algae. It produces the carotenoid astaxanthin, which is used as a colorant in the fish (salmon), food and cosmetics industries. The increased formation of astaxanthin in direct sunlight is exploited.