The seaweed phenomenon in Cancun—primarily dominated by sargassum, a brown macroalgae—is a complex issue driven by oceanic dynamics, human activity, and climate change. Here’s a detailed breakdown of its causes, supported by recent scientific observations and regional data:
1. The “Great Atlantic Sargassum Belt”: A Seasonal Oceanic Phenomenon
Cancun’s seaweed influx stems from a massive, transatlantic algal formation known as the Atlantic Sargassum Belt, which spans over 5,000 miles (8,047 km) from West Africa to the Gulf of Mexico . This belt is not a static “island” but a drifting ecosystem fed by seasonal ocean currents:
- Each year, sargassum begins multiplying in the central Atlantic in early months, then spreads northwest via the North Brazil Current and North Equatorial Current . By April–July, these currents carry dense mats toward the Caribbean, with Cancun’s beaches in Quintana Roo acting as a primary landing point due to the region’s coastal topography .
- The phenomenon has become a “seasonal (new normal)” since 2011, peaking in summer and dissipating by September–October . In 2025, satellite data confirmed another large-scale bloom impacting Cancun and neighboring tourist hubs like the Dominican Republic .
2. Nutrient Pollution: Human Activity Fuels Growth
While ocean currents transport sargassum, eutrophication (excess nutrients in water) is the key driver of its explosive growth. Scientists trace this to two main sources:
- Agricultural Runoff: Industrial farming in Brazil and the Amazon Basin uses massive amounts of synthetic fertilizers rich in nitrogen and phosphorus. These nutrients leach into rivers (e.g., the Amazon) and flow into the Atlantic, creating a “feeding ground” for sargassum . Research on global algal blooms links increased macroalgae (like sargassum) to rising nutrient loads .
- Sewage Discharge: Untreated or partially treated sewage from coastal communities and cruise ships adds additional nitrogen to Caribbean waters, exacerbating algal growth .
3. Climate Change Amplifies the Crisis
Rising global temperatures and atmospheric CO₂ levels further intensify sargassum blooms:
- Warmer sea surface temperatures (SSTs) accelerate algal metabolism and reproduction. A 2024 study noted a positive correlation between SST, CO₂ levels, and macroalgal bloom frequency .
- Ocean acidification, driven by increased CO₂ absorption, may also favor sargassum over other marine species, allowing it to outcompete and dominate coastal ecosystems .
4. Ecological Trade-Offs: A Double-Edged Ecosystem
Importantly, sargassum is not inherently “harmful”—it serves as a critical habitat for sea turtles, commercial fish (e.g., mahi-mahi), and seabirds . However, when it washes ashore in dense quantities, it causes problems:
- As it decomposes, it releases hydrogen sulfide, a gas with a “rotten egg” stench that drives away tourists and harms local tourism (a $30 billion industry in Mexico ).
- Thick mats smother coral reefs and seagrass beds, disrupting the fragile coastal ecosystem that supports Cancun’s biodiversity .
What’s Being Done in Cancun?
Local authorities and businesses have invested in cleanup efforts—In July 2025, teams were photographed removing tons of sargassum from Cancun’s beaches —but long-term solutions remain elusive. Some innovators are turning the crisis into opportunity: Mexican entrepreneurs now process sargassum into biogas, organic fertilizer, and even plant-based leather , though regulatory delays have hindered large-scale adoption.
In short, Cancun’s seaweed problem is a symptom of interconnected global issues: ocean currents move it, human pollution feeds it, and climate change worsens it. Addressing it will require international cooperation on nutrient reduction, sustainable agriculture, and climate action—all while balancing ecological preservation with tourism livelihoods.