Blue-green algae, actually cyanobacteria, form toxic blooms when warm water combines with excess nutrients like nitrogen and phosphorus. These conditions create ideal environments for cyanobacteria to multiply rapidly.
Cyanobacteria thrive in still or slow-moving freshwater systems during hot weather. They absorb sunlight and nutrients from the water, growing exponentially when conditions are right. This creates visible surface scum or mats that resemble algae but are actually bacteria.
The U.S. Environmental Protection Agency notes that cyanobacteria blooms often occur in late summer or early fall when water temperatures peak. These blooms can persist for weeks or even months under favorable conditions.
Excess nutrients enter waterways primarily through agricultural runoff, sewage discharge, and urban stormwater. Fertilizers containing nitrogen and phosphorus wash into lakes and rivers, fueling cyanobacteria growth. A single rainfall event can introduce enough nutrients to trigger a bloom.
For example, the Maumee River in Ohio discharges nutrient-rich water into Lake Erie. This contributes to annual cyanobacteria blooms that affect drinking water supplies for millions of people.
| Common Name | Scientific Name | Toxin Produced |
|---|---|---|
| Microcystis | Microcystis aeruginosa | Microcystins |
| Anabaena | Anabaena flos-aquae | Anatoxins |
| Cylindrospermopsis | Cylindrospermopsis raciborskii | Cylindrospermopsin |
Human activities worsen cyanobacteria problems. Agricultural practices, wastewater treatment inefficiencies, and urban development all increase nutrient loading in waterways. Even well-intentioned actions like over-fertilizing lawns contribute to the problem.
I saw this firsthand when visiting a local lake after heavy rains. The water was covered in greenish scum, and warning signs were posted about potential toxins. This was a direct result of stormwater carrying fertilizers from nearby farms into the lake.
People often confuse cyanobacteria with true algae. While both are aquatic organisms, cyanobacteria are bacteria that obtain energy through photosynthesis, whereas algae are eukaryotic organisms. This distinction is important because cyanobacteria produce harmful toxins that algae typically do not.
Another common misconception is that cyanobacteria blooms only occur in polluted water. While pollution worsens the problem, these bacteria can grow in any water body with sufficient nutrients and warm temperatures.
Reducing nutrient runoff is key to preventing cyanobacteria blooms. Farmers can implement buffer strips along waterways, and municipalities can upgrade wastewater treatment facilities. Individuals can also help by using phosphate-free detergents and limiting fertilizer use.
Understanding what causes blue-green algae helps communities take proactive measures to protect water resources. By addressing nutrient pollution at its source, we can reduce the frequency and severity of these harmful blooms.