overhead view of clouds over a body of water

Special Investigation Links Amazon Destruction to Massive Ocean Algae Bloom

March 30, 2021

Huge, floating beds of brown macro-algae known as sargassum have grown explosively in the Atlantic and the Caribbean over the past decade, swamping beaches, harming tourist economies and greatly altering coastal ecosystems. Until recently, however, the cause of this scourge was a matter of debate.

Now, after years of research, scientists believe they’ve landed on some culprits: The growing discharge of pollutants from the Amazon River, climate change and even dust blown in from the Sahara across the Atlantic in West Africa.

To better explore the origins and effects of this massive sargassum belt – which grows each summer and was already measured as spanning 86 square kilometers in February 2021 -- journalists, remote sensing experts and editors from Brazil, Mexico, Guatemala and the US worked together to study the latest science on the causes of the algae bloom, investigate the sources of growing pollution in the Amazon basin, research the economic and ecological impacts in the Caribbean and put it all together in a compelling series of stories we’ve called “Murky Waters.”

Part 1: Amazon Destruction Linked to the Largest Belt of Algae on the Planet

This scene-setting story looks at the activities producing the main pollutants researchers have identified – deforestation, increased use of fertilizers for agriculture, poor sanitation measures, and the growth of illegal mining activities occurring along the Amazon River and its tributaries. It then highlights the threat sargassum poses to local economies and marine species and warns that similar scenarios are occurring around the globe, meaning, as one researcher put it, “Problems like these create favorable conditions for the explosion of algae populations across the planet.”

Part 2: Brown Tide Threatens Caribbean Coasts and Resorts

The second story in the series takes a more specific, localized look at the ecological and economic threats these sargassum blooms pose to the Caribbean, a mega-diverse region whose tens of millions of inhabitants heavily depend on tourism and natural resources. The coming year looks particularly bad, scientists predict, with one oceanographer warning, “The crisis is coming again for the Caribbean coasts.” (insert graphic)

Part 3: Amazon’s Largest City Dumps Almost Everything in the River

The third story takes readers to Manaus, the largest city in the Amazon region, to reveal a widespread lack of sanitation and extreme wastewater pollution. These conditions can have harmful effects on the health and well-being of local residents, particularly the poorest. But it’s not just people who suffer. As shown in the first story of this series, research provides evidence that large quantities of organic nutrients, such as nitrogen and phosphorous, are reaching the ocean and seeding algae blooms, which can have harmful, even toxic, effects on people and marine life. According to information collected on the origins of nitrogen discharged from the Amazon into the ocean, most comes from untreated sewage.

Part 4: A graphical feature (forthcoming) on mining in the Amazon region – both legal and illegal – has also contributed to contaminating the river, not just with organic pollutants but also with toxic, heavy metals.

This series was produced by GeoJournalism media outlet InfoAmazonia and an independent journalist in Mexico with support from the Earth Journalism Network and in partnership with Earthrise Media. 

It was the result of a year-long reporting endeavor that took place despite the restrictions imposed by the Covid-19 pandemic, with the first story published simultaneously on NOLA.com (in English), Aristegui Noticias (in Spanish) and InfoAmazonia (in Portuguese, Spanish and English).

Although it was challenging to coordinate the publication across multiple languages and countries, we believe this gave it greater impact, and EJN is eager to foster similar cross-border collaborations in the future.

You can read the entire series and the translations at our special report page here.

(Banner photo: The Amazon River disgorges a plume of sediment into the Atlantic Ocean. The river sends an average of 273,361 cubic yards of water into the ocean every second / Credit: ESA Copernicus/ Sentinel-3 / produced by Earthrise)