Blue-green algae, photosynthetic bacteria, freshwater blooms, cyanotoxins, microcystin, nitrogen fixation, lakes, reservoirs, mats, water treatment, pets, harmful algal blooms, nutrient pollution, eutrophication, public health, and ecosystem change
Cyanobacteria
Cyanobacteria are photosynthetic bacteria found in water and moist environments; some species can form harmful blooms and produce toxins.
What cyanobacteria are
Cyanobacteria are ancient photosynthetic bacteria. They live in lakes, rivers, reservoirs, oceans, soils, rocks, and damp surfaces. In everyday water-quality work, people often notice them when they form green, blue-green, or paint-like blooms on freshwater.
Why they are called blue-green algae
The nickname comes from their color and their ability to photosynthesize. Biologically, though, cyanobacteria are bacteria, not algae. That distinction matters because their cells, toxins, and bloom behavior are not the same as every other algal group.
Blooms
Cyanobacteria can multiply quickly when water is warm, calm, nutrient-rich, and sunny. Blooms may look like pea soup, spilled paint, floating mats, streaks, or small green particles. Wind can push blooms into shorelines where people and pets are more likely to contact them.
Cyanotoxins
Some cyanobacteria produce toxins, including microcystins and other compounds that can affect the liver, nervous system, skin, stomach, or respiratory system. A bloom cannot be judged safely by appearance alone because toxicity depends on the species and conditions.
Ecological roles
Cyanobacteria are not simply villains. They helped oxygenate Earth’s atmosphere long ago, contribute to food webs, and some can fix nitrogen from the air. The problem begins when growth becomes excessive or toxic in places people and ecosystems depend on.
Water supplies and recreation
Blooms can close beaches, affect drinking-water treatment, create taste and odor problems, and endanger pets or livestock that drink contaminated water. Boiling water does not reliably remove many cyanotoxins and can concentrate some toxins as water evaporates.
Monitoring and prevention
Managers use visual reports, satellite imagery, water sampling, toxin tests, and public advisories. Prevention usually focuses on reducing nutrient pollution, slowing runoff, improving wastewater and stormwater management, and warning people quickly when blooms appear.
Why it matters
Cyanobacteria sit at a strange crossroads: essential to Earth history, useful in many ecosystems, and dangerous when bloom-forming species release toxins. Understanding them helps separate normal water life from conditions that require public-health action.