Euglena is a common member of the euglenoid flagellates, which are mostly single-celled with one or a few flagella that help them swim. Euglena has many green chloroplasts, and lumpy white carbohydrate storage bodies in its cells. This alga is common in waters that contain a lot of dissolved organic material, including vitamins. Like people, Euglena has to take its vitamins or it cannot survive. Euglenoids are most abundant at the air-water interface or the bottom waters. If a water sample has a lot of Euglena or similar algae in it, you can assume that the water has a relatively high organic content.

Each cell of a Volvox colony has two flagella, and their movement must somehow be coordinated or the colony would never be able to swim anywhere. As it swims, Volvox entertainingly tumbles through the water. Its ability to swim allows Volvox to move up and down in the water column, to find mineral nutrients (much like a grocery shopping expedition). Volvox inhabits ponds and lakes of moderate mineral nutrient content.

Micrasterias, whose name comes from Greek words meaning "small star," is appropriately named. Each cell has two parts (semi-cells) linked by a narrow bridge where the cell nucleus (the clear circle) resides. This alga, and its relatives, known as desmids, are most common and abundant in waters having low mineral nutrient content, particularly peat bog waters. Many desmids can jet through the water by squirting jelly through small pores in their cell wall. Others have a jelly coating that is home to many kinds of bacteria that may be beneficial algae

Freshwater dinoflagellates, illustrated here by Peridinium, may have golden plastids, blue-green plastids, acquired by ingesting cryptomonads, or may be completely without plastids, Many, even the photosynthetic types, ingest bacteria, small eukaryotic algae, and other particles from the water. They are exceptions to separation of plankton into heterotrophic ("other feeding") and autotrophic ("self feeding, photosynthetic) groups. While several marine dinoflagellate species are known to produce toxins and be responsible for fish kills and illness in humans and aquatic mammals, freshwater dinoflagellates seem to be harmless. The reason for this important difference is unknown!

Synura, a representative of the golden algae, is most numerous in water whose mineral content is so low that many zooplankton that would normally feed voraciously on golden algae, are present in only low numbers.