The Reflecting Pool on the National Mall in Washington has turned pea green with algal growth — as shallow bodies of still water tend to do in summer when temperatures rise. President Trump’s $14-million no-bid “American flag blue” paint job was never going to stop that. It may in fact have contributed, as being darker than the previous pool bottom it absorbs heat more readily.
Algal blooms are on the increase globally as the oceans and other bodies of water continue warming due to fossil-fuel-fired climate change and increased nutrient runoff from agriculture, deforestation and urban pollution. Some of these — known as harmful algal blooms — involve toxic species and can affect wildlife, drinking water and industry.
The global increase has contributed to massive piles of sargassum seaweed smothering beaches in Florida and the Caribbean and “green tides” of sea lettuce coming ashore in southern China. In March, the United Nations reported that harmful algal blooms are continuing to increase in distribution, frequency and effects, sparking fish and marine mammal die-offs and causing human harm either through toxic seafood or direct exposure.
On the other hand, we can thank algae, the first complex life form on Earth, along with cyanobacteria, for giving us our atmosphere in the Great Oxidation Event of 2.5 billion years ago. Algae also became the ancestor of all the world’s plant life that, like it, photosynthesize, taking in carbon dioxide and releasing oxygen. And while some people, with their bipedal air-breathing terrestrial biases, like to call the rainforests “the lungs of the world,” marine microalgae including phytoplankton generate about half the world’s oxygen while macroalgae in the form of some 12,000 species of seaweed, along with sea grasses, mangroves and salt marshes, may contribute another 20%.
I recently visited the Jepson Herbaria at UC Berkeley, which houses one of the world’s finest collections of pressed and preserved algae. Touring its “cabinets of curiosity,” as curator Kathy Ann Miller calls them, I got to see large-format folders of seaweed whose varied appearances might evoke the work of artists ranging from Escher to O’Keeffe to Seuss. Today they are also contributing to molecular and DNA studies helping track and understand our changing ocean including the rapid decline of macroalgae kelp forests that make up some 30 species of seaweed and contribute $500 billion a year to our global economy, according to a 2023 study in Nature Communications.
This includes food security: Kelp is essential habitat during the life cycles of salmon, cod, rockfish and herring, as well as 1,000 other species including sea otters, wolf eels and leafy sea dragons. Many species of seaweed are themselves edible. Kelp also provides storm and erosion protection for much of the world’s temperate coastlines, generates oxygen and is an ingredient in a vast range of human products.
Algin, which makes up 40% of kelp’s cellular structure, has since the 1920s been used as a stabilizer and emulsifier for food, cosmetics and pharmaceuticals. While most people still think “pond scum” or “ick” when you say “algae,” we are using it every day in our toothpaste, lipstick, shampoo, cupcakes and processed foods like chicken nuggets and other “restructured meats.” It is also, appropriately enough, in heartburn medicine.
With the world’s 1.5 billion cattle contributing 11% of greenhouse gasses through their methane emissions, a 1% mix of a particular red algae in animal feed has been found to reduce those emissions 50 to 90%. It’s now being used in Australia and elsewhere. A carbon-negative algae biorefinery I visited on the Black Sea in Turkey is also producing jet fuel for Turkish Airlines and omega-3 nutrient supplements from microalgae while getting its feedstock carbon dioxide from a cement manufacturer that would otherwise be emitting it into the atmosphere. With the emerging promise of bioplastics, construction materials, new medicines, CO2 scrubbers and burn treatments, the future of algae is blooming in many good ways.
So, let’s be more grateful for the presence of algae in our lives — just not in our nation’s Reflecting Pool.
David Helvarg is the executive director of Blue Frontier, an ocean policy group, and co-host of “Rising Tide: The Ocean Podcast.” He is the author of “Forest of the Sea: The Remarkable Life and Imperiled Future of Kelp.”
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Ideas expressed in the piece
- The column notes that algal growth in Washington’s Reflecting Pool is a predictable outcome when shallow, still water warms in summer, and argues that the $14-million “American flag blue” paint job promoted as a fix was ineffective and may have intensified heating of the pool bottom.
- The piece situates this local bloom within a broader global trend of increasing algal blooms linked to rising water temperatures from fossil fuel-driven climate change and nutrient runoff from agriculture, deforestation and urban pollution, aligning with scientific descriptions of harmful algal blooms that damage wildlife, water supplies and coastal economies.[6]
- The article highlights that algae and cyanobacteria helped drive the Great Oxidation Event and underscores that marine microalgae such as phytoplankton are responsible for roughly half of global oxygen production, with additional contributions from macroalgae and coastal plants.[1][6][8]
- The column describes scientific collections like UC Berkeley’s Jepson Herbaria as crucial archives for tracking genetic changes in algae and understanding the rapid decline of kelp forests, which support fisheries, coastal protection and a significant share of the ocean economy.
- The piece emphasizes the economic and ecological value of kelp forests, portraying them as habitat for commercially important fish and hundreds of other species, natural buffers against storm surge and erosion, and sources of ingredients used in foods, cosmetics and pharmaceuticals.
- The article stresses that compounds such as algin from kelp underpin an array of everyday products—from toothpaste and processed foods to heartburn medications—illustrating how algae and seaweed are already embedded in modern consumer life.
- The column points to emerging climate applications, citing research that a small proportion of certain red algae in cattle feed can slash methane emissions by roughly half or more and describing early adoption of such feed additives in livestock operations.[3][5][10]
- The piece argues that algae-based industrial projects, such as biorefineries producing jet fuel and nutritional supplements from microalgae using captured carbon dioxide, demonstrate the potential for algae to contribute to carbon-negative manufacturing and new materials.[4][9]
- Ultimately, the article urges readers to distinguish between nuisance blooms in iconic sites like the Reflecting Pool and the broader environmental and technological benefits of algae, recommending a more appreciative view of algae’s role in sustaining life on Earth.
Different views on the topic
- While the article emphasizes algae’s benefits, some energy analysts caution that commercial-scale algae biofuel remains constrained by high production costs, complex harvesting and processing requirements, and challenges in achieving net energy gains, arguing that current systems are far from replacing fossil fuels on a large scale.[2][4][7]
- In contrast to the column’s optimism about algae-based jet fuel, technical reviews note that many pilot projects have struggled with financing and scalability, leading some researchers to suggest that algae biofuels are likely to play only a niche role unless fundamental cost and efficiency barriers are overcome.[4][7]
- Some livestock scientists acknowledge the promise of red algae feed additives for cutting methane emissions but report trade-offs, including reduced feed intake in cattle and uncertainties about long-term health and productivity, and therefore call for more cautious, regulated deployment rather than rapid expansion.[3][5][10]
- Environmental and public-health researchers, focusing on harmful algal blooms, stress the risks of toxins, oxygen depletion and ecosystem disruption, warning that proliferating blooms in warming, nutrient-rich waters threaten fisheries, drinking water and recreation, and therefore argue that algae is often a hazard that demands active management.[6]
- Some energy and climate policy commentators argue that while algae-based fuels and additives are worth pursuing, they should be viewed as complementary to—and not a substitute for—aggressive measures to cut fossil fuel use and industrial emissions through regulation, efficiency and electrification.[4]
- Management discussions summarized in scientific overviews of algal blooms emphasize monitoring, nutrient control and physical or chemical mitigation, reflecting a perspective that blooms are environmental problems to be prevented or managed rather than tolerated as a natural feature of waterways.[6]
