| Classification | Common genera of interest | Biological characteristics | Importance |
| Cyanobacteria (blue-green algae) | Anabaena, Aphanizomenon, Cylindrospermopsis, Lyngbya, Microcystis, Oscillatoria, Phormidium, Planktothrix | • Cell walls are composed of peptidoglycan and a layer of lipopolysaccharide (Gram-negative) • Pigments include chlorophylls, phycobilins, and carotenoids • Contain specialized structures: aerotopes, heterocytes, and akinetes • Various morphologies: unicellular, colonial, filamentous | • Produce cyanotoxins (cyclic peptides, alkaloids, and endotoxins) • Produce T&O compounds • Clog water intake and filter • Increase in organic matter |
| Chlorophyta (green algae) | Chara, Cladophora, Hydrodictyon, Pithophora, Scenedesmus | • Have flagella in at least one life stage • Various morphologies: unicellular, colonial, filamentous | • Some genera produce T&O compounds |
| Bacillariophyta (diatoms) | Aulacoseira, Cyclotella, Melosira, Nitzschia, Pseudonitzschia, Synedra, Tabellaria | • Cell walls are made of silica • Two forms: centric and pennate • Many have spines or stellate | • Only one marine genus (Pseudonitzschia) produces a toxin (domoic acid) • Some genera produce T&O compounds |
| Dinophyceae (dinoflagellates) | Ceratium, Peridinium | • Unicellular with two dissimilar flagella • Many have lorica made of cellulose | • Many marine genera produce toxins • Only one freshwater toxin-producing species (Peridiniopsis polonicum) • Some genera produce T&O compounds |
| Chrysophyceae (golden algae) | Chrysosphaerella, Dinobryon, Uroglen | • Unicellular with one or two dissimilar flagella • Unique siliceous cyst • Some have lorica | • Some genera produce T&O compounds |
| Euglenophyceae (euglenoids) | Euglena, Phacus | • Generally, spindle-shaped • No cell walls, but enveloped by a proteinaceous pellicle | • A few species (e.g., Euglena sanguinea) produce a toxin (euglenophycin) |
| Haptophyta | Prymnesium | Usually with two flagella and a unique haptonema | • Prymnesium parvum produces a toxin (prymnesin) |
| Phaeophyceae Xanthophyceae Rhodophyta |
| • Commonly known as brown, yellow-green, and red algae, respectively. | • Rarely in large quantities, not a concern |