Algae blooms: Unsightly for the Reflecting Pool, potentially toxic elsewhere

Algae blooms: Unsightly for the Reflecting Pool, potentially toxic elsewhere Ketura Persellin June 25, 2026 Algae is making headlines after the Trump administration’s $14.2 million renovation of the Lincoln Memorial Reflecting Pool turned its water closer in color to the Chicago River on St. Patrick's Day – an unmistakable bright green . But the color of the Reflecting Pool came not from thousands of tons of green dye but from an algae bloom consuming the 6.5 million gallon basin. Over half of all U.S. lakes now suffer from worsening algae blooms , a problem that has intensified dramatically since 2015. Not all algae blooms are toxic, and that includes the current reflecting pool growth. It’s the toxic blooms elsewhere that prompt health concerns. A toxic algae bloom is not algae at all. It’s an overgrowth of algae-like bacteria in an aquatic ecosystem. It can kill fish, birds and other wildlife, and cause severe kidney and degenerative diseases in humans. It’s impossible to know by sight alone whether an algae bloom is toxic. Green-blue scum, thick mats on the water’s surface, or foul odors can signal danger. But the problem often starts upstream, when fertilizer, manure and climate-driven runoff fuel rapid algae growth. Health impacts of toxic algae In freshwater systems, harmful algae blooms are produced by blue-green algae, or cyanobacteria. Algae blooms can exist during part of the year before they become toxic. Toxins produced by harmful algae blooms can enter the body through three main pathways : skin absorption, consumption of contaminated drinking water and breathing in airborne particles, which can drift for miles. In 2022 alone, the latest year for which the data is available, the Center for Disease Control and Prevention found that harmful algae blooms resulted in 95 human and over 102,000 animal illnesses. In Michigan’s Lower Peninsula, four dogs died soon after drinking toxic pond water. They had shown symptoms of exposure such as vomiting and complete loss of coordination, followed by a rapid deterioration. These outbreaks also have major economic and community costs : swimming advisories go up and beaches close. Water recreation, including tourism and fishing, halts, lakes require testing and treatment, and health risks strain local healthcare systems. One estimate puts the cost of freshwater harmful algae blooms in the U.S. at $4.6 billion each year. Identifying harmful algae blooms No single federal body oversees harmful algae blooms. The Environmental Protection Agency and the National Oceanic and Atmospheric Administration collaborate to monitor some algae blooms across the U.S.. But the agencies lack a complete set of data because there are too many bodies of water to monitor. Real-time monitoring on cyanobacteria blooms ended in 2024. At the state level, monitoring and warning programs exist unevenly across the U.S. In 2019, the Natural Resources Defense Council rated each state on the effectiveness and extent of their algae bloom monitoring and outreach programs, determining that 16 states still did not collect any data and 40 states did not provide that data online. It’s impossible to tell for sure if an algae bloom is toxic just by looking at it. These signs may indicate toxicity: A strong, unpleasant odor, like rotten eggs or rotting plants Green or bluish green scum that looks like spilled paint, or mats/globs of algae What should you do if you think you see a harmful algae bloom? Avoid contact with the water or foam in or near the water, and keep pets away, too. Rinse off immediately with soap and warm water if you’ve touched an algae bloom or water near the algae. Avoid contaminated fish or shellfish from ecosystems experiencing a harmful algae bloom. Notify your county or state health officials if you’ve experienced respiratory or other health symptoms after being near an algae bloom. How manure and fertilizer drive toxic blooms Harmful algae blooms are often caused by human practices. Agricultural inputs, like animal manure and chemical fertilizers, are one of the primary culprits . The problem often begins with factory farms and major commodity crop farms. Factory farm animals produce huge amounts of manure every year, which is then spread, along with synthetic fertilizers, on nearby crop fields . Both can run off from farm fields into nearby waterways, raising the levels of nitrogen and phosphorus, feeding the blue-green algae and causing potentially toxic blooms to flourish. Climate change also worsens the problem of algae blooms. Hotter temperatures driven by intensifying climate change exacerbate cyanobacteria growth. The climate crisis has made rainfall events more severe and frequent, driving increased agricultural runoff to rivers, streams, and lakes. Higher carbon dioxide levels feed toxic algae species, which need it to survive. Since 2015, the number of toxic algae bloom advisories and closures has increased every single year. The Midwest, because of its concentration of industrial farming operations, is particularly at risk. An EPA-led study found that 56% of Midwestern lakes near agriculturally dominated areas exceeded World Health Organization cyanobacteria concentration limits. Policies to reduce nutrient pollution There isn’t one simple solution to the problem of toxic algae blooms. Crop farms could help mitigate their occurrence by using conservation practices that reduce runoff: cover crops, diversified crop rotations and grass buffers near bodies of water. Keeping livestock away from rivers and streams and matching fertilizer or manure amounts to crop needs can also help. Agriculture Department conservation programs could help fund farmers’ use of these practices, but the programs are oversubscribed , so many of the farmers who apply for funding don’t get it. Areas of Focus Farm Pollution Guest Authors Adam Levin June 25, 2026