Toxic Algae Bloom Hits South Africa’s Hartebeespoort Dam

NASA satellite imagery has revealed the scale of harmful algal blooms (HABs) at South Africa’s Hartbeespoort Dam, highlighting significant water quality concerns and potential health risks to nearby human communities, and animals.

The imagery, which forms part of an animation tracking changes at the dam between June 2022 and July 2023, shows vivid green swirls of algae and invasive aquatic plants spreading across the reservoir. These masses grow, drift across the water, and eventually fade before returning again.

The data was compiled using the Harmonized Landsat and Sentinel-2 (HLS) product. This NASA product combines imagery from the NASA/USGS Landsat 8 and Landsat 9 satellites and the European Space Agency’s Sentinel-2A, 2B, and 2C satellites.

The Risks of Cyanobacteria

The green masses in the reservoir often contain cyanobacteria, also known as blue-green algae. While photosynthetic organisms are generally vital for maintaining healthy ecosystems, they become hazardous when they multiply too rapidly.

These outbreaks are classified as harmful algal blooms. Some HABs are toxic and can produce substances that are dangerous to humans and animals, threatening the environments they support.

Beyond the direct toxicity of the algae, these blooms can lead to severe ecological degradation. As large algal blooms die off, bacteria break them down and consume the available oxygen in the water.

This process can lead to hypoxia, a state of dangerously low oxygen levels. Hypoxia can result in the death of fish and other aquatic life, further destabilizing the reservoir’s ecosystem.

Nutrient Pollution and Eutrophication

The proliferation of these blooms is often the result of eutrophication. This process begins when an ecosystem is overloaded with nutrients, typically due to agricultural runoff and other human-driven inputs.

Phosphorus from wastewater and agricultural runoff are specifically cited as triggers that enter rivers and dams, fueling the rapid growth of algae.

NASA scientist Bridget Seegers, who studies cyanobacteria in freshwater ecosystems, compares this environmental phenomenon to over-fertilising a garden.

Regarding the relationship between nutrient levels and algal growth, Seegers stated, If you add a lot of nutrients, you’re going to have a lot of growth.

Environmental Impact

The presence of these blooms indicates environmental stress and nutrient pollution within the Hartbeespoort Dam. The resulting water quality woes affect not only the aquatic life but also the human populations that rely on or live near the reservoir.

The satellite tracking provided by NASA and the European Space Agency allows for the monitoring of how these blooms move and fade over the course of a year, providing a visual record of the dam’s ongoing struggle with water quality.