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.”

©2026 Los Angeles Times. Visit at latimes.com. Distributed by Tribune Content Agency, LLC.