- Planet Earth
A 2022 satellite photo shows a thick mat of blooming algae and invasive aquatic plants spreading across the surface of the reservoir at South Africa's Hartebeespoort Dam. The verdant mass is both toxic and capable of depleting the water's oxygen levels.
When you purchase through links on our site, we may earn an affiliate commission. Here’s how it works.
Vibrant, verdant masses of algae and invasive aquatic plants frequently cover the surface of the reservoir at South Africa's Hartebeespoort Dam.
(Image credit: NASA/Landsat 8)
- Copy link
- X
Get the world’s most fascinating discoveries delivered straight to your inbox.
Become a Member in Seconds
Unlock instant access to exclusive member features.
Contact me with news and offers from other Future brands Receive email from us on behalf of our trusted partners or sponsors By submitting your information you agree to the Terms & Conditions and Privacy Policy and are aged 16 or over.You are now subscribed
Your newsletter sign-up was successful
Want to add more newsletters?
Delivered Daily
Daily Newsletter
Sign up for the latest discoveries, groundbreaking research and fascinating breakthroughs that impact you and the wider world direct to your inbox.
Signup +
Once a week
Life's Little Mysteries
Feed your curiosity with an exclusive mystery every week, solved with science and delivered direct to your inbox before it's seen anywhere else.
Signup +
Once a week
How It Works
Sign up to our free science & technology newsletter for your weekly fix of fascinating articles, quick quizzes, amazing images, and more
Signup +
Delivered daily
Space.com Newsletter
Breaking space news, the latest updates on rocket launches, skywatching events and more!
Signup +
Once a month
Watch This Space
Sign up to our monthly entertainment newsletter to keep up with all our coverage of the latest sci-fi and space movies, tv shows, games and books.
Signup +
Once a week
Night Sky This Week
Discover this week's must-see night sky events, moon phases, and stunning astrophotos. Sign up for our skywatching newsletter and explore the universe with us!
Signup +Join the club
Get full access to premium articles, exclusive features and a growing list of member rewards.
Explore An account already exists for this email address, please log in. Subscribe to our newsletter QUICK FACTSWhere is it? Hartbeespoort Dam, North West province, South Africa [-25.74486936, 27.858152164]
What's in the photo? A vivid-green bloom of toxic algae and planets spreading across a reservoir
Which satellite took the photo? Landsat 8
When was it taken? Aug. 10, 2022
This striking satellite snap shows a verdant mass of algae and other aquatic plants sprawling across the surface of a recreational reservoir in South Africa. This frequent phenomenon releases toxic chemicals into the water and gives rise to hidden "dead zones" that can cause widespread fish fatalities.
Most large bodies of water experience seasonal blooms, where photosynthetic algae, or cyanobacteria, rapidly multiply and spread across their surfaces due to changes in weather or nutrient inflow. However, the Hartbeespoort reservoir is in a constant state of "hypereutrophication," which means it has an overabundance of nutrients, such as nitrogen and phosphorus. As a result, the blooms there are much more frequent and intense, according to NASA's Earth Observatory.
You may like-
Rainbow-colored phantom lakes emerge around Namibia's 'Great White Place'
-
Trippy 'biomass' snap reveals first detailed look at our planet's carbon stores
-
Extreme blast of Arctic air from polar vortex paints a picturesque plume off Florida coast
"On clear days … satellite images often reveal a reservoir with shades of deep blue interrupted by drifting patches of vivid green," Earth Observatory representatives wrote.
However, it is not just algae that bloom across the reservoir's surface. The verdant masses also include aquatic plants, including water hyacinths (Pontederia crassipes) and Salvinia minima, both of which are invasive species and grow across the reservoir's surface in large, intertwined mats.
Eutrophication occurs when too many nutrients are added to a body of water, often due to human influences, and can lead to unnaturally large algal blooms. "It's like having a garden," Bridget Seegers, an oceanographer at Goddard Space Flight Center in Maryland who leads NASA's Cyanobacteria Assessment Network, told the Earth Observatory. "If you add a lot of nutrients, you're going to have a lot of growth." (Hypereutrophication is a more extreme version of this phenomenon.)
However, unlike in a garden, you cannot simply cut back the blooms you don't want, and the consequences of not being able to contain the plant life are much more severe. For example, some of the algae within the Hartbeespoort reservoir can produce toxins that must be filtered out of the water for it to be safe to drink.
Sign up for the Live Science daily newsletter nowContact me with news and offers from other Future brandsReceive email from us on behalf of our trusted partners or sponsorsBy submitting your information you agree to the Terms & Conditions and Privacy Policy and are aged 16 or over.However, the bigger issue is that the excessive growth of plant life on the surface sucks up the oxygen from the water below, making it toxic to fish that need to extract oxygen from water via their gills to breathe. These areas of oxygen-poor water are often dubbed "dead zones," and when the blooms spread widely, there are few safe spaces for the fish to go.
In April 2023, a lack of oxygen in part of the reservoir was linked to a mass die-off of fish, including hundreds of large carp, according to a government report. And in November 2025, another bloom likely triggered a similar die-off and left fish "gasping for air" at the reservoir's surface, according to South Africa-based News 24. These blooms eventually disappear, but the next one is rarely far behind.
The Hartbeespoort reservoir has experienced near-continuous hypereutrophication since the 1970s, excluding a brief period in the 1990s when a successful bioremediation program was introduced but then was quickly scrapped due to high costs. As a result, algae have been blooming constantly, spreading and dying across the reservoir's surface for decades.
You can see this in the animation below, which was made from aerial images collected by the Landsat 8, Landsat 9 and Sentinel satellites between June 2022 and July 2023.
A 2023 study that analyzed data from the previous four decades found that the main culprit was the Crocodile River, which has become extremely polluted with runoff from farms and golf courses that use nutrient-rich fertilizers.
In addition to threatening wildlife, the toxins in the water have been known to cause rashes on water-sports enthusiasts and sicken dogs.
See more Earth from space
Mystery swirls in the Baltic Sea
A 2018 satellite photo shows an unknown substance swirling across the Gulf of Gdańsk in Poland. Scientists were shocked to discover what it really was.
Toxic bloom in Nevada
A 2024 satellite photo shows an unusually active bloom of toxic cyanobacteria swirling in the water of Nevada's Pyramid Lake. Research suggests that the algae has been blooming there for at least 9,000 years.
Milky spirals in Turkish lake
A 2016 astronaut photo shows surprising plumes of milky material swirling in the waters of Turkey's Lake Van — the largest alkaline lake on Earth.
TOPICS Earth from space
Harry BakerSocial Links NavigationSenior Staff WriterHarry is a U.K.-based senior staff writer at Live Science. He studied marine biology at the University of Exeter before training to become a journalist. He covers a wide range of topics including space exploration, planetary science, space weather, climate change, animal behavior and paleontology. His recent work on the solar maximum won "best space submission" at the 2024 Aerospace Media Awards and was shortlisted in the "top scoop" category at the NCTJ Awards for Excellence in 2023. He also writes Live Science's weekly Earth from space series.
View MoreYou must confirm your public display name before commenting
Please logout and then login again, you will then be prompted to enter your display name.
Logout Read more
Planet Earth
Rainbow-colored phantom lakes emerge around Namibia's 'Great White Place'
Planet Earth
Trippy 'biomass' snap reveals first detailed look at our planet's carbon stores
Rivers & Oceans
Extreme blast of Arctic air from polar vortex paints a picturesque plume off Florida coast
Archaeology
World's oldest rock art, giant reservoir found beneath the East Coast seafloor, black hole revelations, and a record solar radiation storm
Rivers & Oceans
3 rivers merge into striking half-and-half waterway in Guyana
Rivers & Oceans
Giant underwater plumes triggered by 7-story waves at Nazaré captured off Portuguese coast
Latest in Planet Earth
Climate change
Earth's energy imbalance is much more extreme than climate models show — but scientists aren't sure why
Climate change
California declared war on smog in the 1970s. The knock-on effects were huge.
Climate change
Antarctica hides huge caches of gold, silver, copper and iron. As the ice melts, countries may race to harvest them.
Climate change
Extreme wildfires, droughts and storms could happen even under moderate global warming, study finds
Climate change
China's huge push to reduce air pollution had an unexpected consequence in the Arctic
Rivers & Oceans
Scientists discover potentially huge freshwater reservoir hidden beneath Great Salt Lake
Latest in Features
Space
NASA telescope uncovers new mystery in supernova first spotted by Chinese astronomers 2,000 years ago — Space photo of the week
Genetics
Are allergies genetic?
Ancient Egyptians
Beadnet dress: A 4,500-year-old ancient Egyptian funeral 'gown' that was in vogue during the Old Kingdom
Space
Hubble images taken 25 years apart show big changes in the iconic Crab Nebula — Space photo of the week
Rivers & Oceans
Lençóis Maranhenses: Brazil's dune-filled expanse that sits at the intersection of 3 biomes
Planet Earth
DNA shed by every living thing is lurking in the environment — and it could tell us how Earth is changing in real time
LATEST ARTICLES- 1California declared war on smog in the 1970s. The knock-on effects were huge.
- 2Laifen Wave Pro electric toothbrush review: A perfect all-rounder
- 3Physicists moved volatile antimatter by truck for the first time ever — paving the way for groundbreaking new research
- 4Deadly, vivid-green mass sprawls across South African reservoir
- 5The Artemis II astronauts have just flown farther from Earth than any humans in history
