Coral reefs are powerful, resilient ecosystems supporting 25% of all marine list and over a billion people globally. But these ecosystems are fragile and pollution is one of the most immediate threats they face. While climate change grabs headlines (and is still very important), local pollution is doing some serious damage in weakening coral defenses and accelerating decline.
These aren’t distant problems. They’re happening now—and they’re reversible. Here’s how different types of pollution directly impact coral reefs and what we can do to stop the damage.
Nutrient Pollution Overfeeds the Ocean
Imagine dumping fertilizer into a tropical garden nonstop—eventually, things overgrow, choke each other out, and die. That’s what happens when excess nutrients like nitrogen and phosphorus enter coastal waters. These nutrients come from agricultural runoff, leaking septic systems, and untreated sewage. And they don’t just disappear.
Once in the ocean, they act as fuel for algae. The result? Massive blooms that blanket coral reefs, block out sunlight, and outcompete corals for space. When these algae die, they decompose and consume oxygen from the water, creating low-oxygen “dead zones” where coral and fish struggle to survive.
Worse, these conditions invite pathogens. Nutrient pollution has been linked to spikes in coral diseases like white syndrome and black band disease, which can spread rapidly across entire reef systems.
Main sources
- Fertilizers and manure from farms and lawns
- Poorly treated sewage and septic overflow
- Rainwater runoff from cities and roads
Impact on reefs
- Algal overgrowth that smothers coral
- Increases risk of coral disease and mortality
- Lower oxygen levels and light availability
What you can do
Support wastewater upgrades and local clean water initiatives. At home, choose organic or low-phosphorus products and be mindful of what goes down your drain.
Sediment Turns Coral Reefs Into Dustbowls
Healthy coral reefs need clean water—sunlight powers their symbiotic algae, which feed the corals from within. But when land-based sediment washes into the ocean, it clouds the water and settles on reef surfaces like a suffocating blanket.
This sediment usually comes from poorly managed construction sites, deforested areas, and overgrazed pastures. With no vegetation to hold soil in place, rain sweeps mud and debris into rivers that lead straight to the sea.
Once it reaches the reef, sediment does real damage. It blocks light, preventing photosynthesis. It clogs coral mouths, interfering with feeding. And it makes it harder for coral larvae to settle and grow—slowing reef recovery and disrupting the delicate balance of life.
Read about our work in Maui to reduce sedimentation smothering the reef >
Main sources
- Land clearing and construction
- Unregulated agriculture
- Erosion from poorly managed landscapes
Impact on reefs
- Reduces sunlight critical for coral survival
- Smothers coral polyps and disrupts feeding
- Hinders growth and reef regeneration
What you can do
Support smart coastal development and reforestation. When traveling or living near the coast, look for businesses that practice sustainable land management.
Plastic Waste Brings Disease
It’s easy to think of plastic pollution as a surface problem—bottles bobbing in the waves, nets tangled in sea turtles. But look closer beneath the surface, and you’ll find plastic has become a chronic threat to coral reefs. It’s showing up in the most remote places on Earth—reef systems once considered untouched now littered with debris.
Floating plastic doesn’t just ruin the view. As it drifts through the ocean, it collides with coral structures, scraping delicate polyps and creating wounds that leave them vulnerable to infection. Larger debris, like discarded fishing gear or plastic bags, can get snagged on the reef, physically breaking coral branches and blocking sunlight.
But the problem goes deeper—literally. As plastic breaks down, it releases microscopic fragments called microplastics, and these aren’t just inert particles. Scientists have discovered that microplastics act like little rafts for harmful bacteria and pathogens. When these bacteria-laden plastics make contact with coral, they dramatically increase the risk of disease—up to 89% higher, according to some studies.
One particularly insidious effect is how plastic changes the coral microbiome—the collection of beneficial bacteria that help coral stay healthy. Disrupting this microbial balance makes coral more susceptible to stress, disease, and bleaching. And unlike a one-time event like an oil spill, plastic keeps accumulating. It never truly goes away.
Main sources
- Single-use plastics (bags, wrappers, packaging)
- Abandoned or lost fishing gear
- Microfibers from clothing, cleaning cloths, and hygiene products
Impact on reefs
- Cuts, abrasions, and physical damage to coral
- Reduced sunlight exposure
- Increased rates of disease and infection
- Disrupted coral microbiome
What you can do
Reducing plastic use might feel small, but it makes a big difference. Choose reusable items over disposables, avoid products with microbeads or glitter made from plastic, and support local and global efforts to reduce marine plastic pollution.
Oil and Chemicals Poison the Reef One Drop at a Time
We often think of oil spills as rare catastrophes—but oil and chemical pollution happen every day in smaller ways. Storm drains flush chemicals from roads, lawns, and factories straight into the sea. Farms spray pesticides that wash into coastal waters. Even tiny spills from boats add up over time.
Oil is especially toxic to coral. It coats their surface, suffocates polyps, and interferes with reproduction. Juvenile corals are particularly vulnerable, with exposure often leading to stunted growth or death. Chemical pollutants like mercury, lead, and pesticides accumulate in reef species, weakening coral and the creatures they shelter.
Unlike physical damage, these toxins often linger—building up in the reef’s food web and altering life on a microscopic level. In high enough concentrations, they can wipe out entire reef sections and make recovery nearly impossible.
Where it comes from
- Oil spills, fuel leaks, and marine transport
- Pesticides, herbicides, and industrial waste
- Household chemicals and automotive runoff
Why it matters
- Interferes with coral reproduction and growth
- Kills coral larvae and juvenile reef species
- Contaminates reef food webs and ecosystems
What you can do
Dispose of chemicals properly and avoid toxic pesticides. Support policies that hold polluters accountable and invest in safer, cleaner alternatives.
Sunscreen Is a Silent Coral Killer
Most people don’t think twice about slathering on sunscreen before diving into the ocean—but what protects our skin can be deadly to coral reefs. Many commercial sunscreens contain chemicals like oxybenzone and octinoxate, which have been shown to cause coral bleaching, deform coral larvae, and damage DNA.
Don’t miss the other 6 harmful ingredients. You can read more in our article Sunscreen 101 >
These effects can happen at incredibly low concentrations—just a single drop in a swimming pool-sized area of water can be enough to disrupt coral development. The chemicals wash off swimmers, rinse down the drain in showers, and end up in the ocean through wastewater systems.
Over time, this chemical cocktail builds up in coastal areas, especially in popular tourist zones. Even reefs that appear healthy can be silently weakened by long-term chemical exposure.
Where it comes from
- Chemical sunscreens used by swimmers and divers
- Wastewater and stormwater runoff
Why it matters
- Causes bleaching and tissue damage
- Disrupts coral hormones and DNA
- Reduces coral resilience and reproductive success
What you can do
Switch to mineral-based sunscreen with non-nano zinc oxide or titanium dioxide. Wear sunshirts and dive skins for sun protection. These alternatives protect your skin without harming the reef.
A Cleaner Ocean Starts With Us
Pollution is a complex problem, but the solutions are within reach. At CORAL, we work with communities to reduce local threats—from upgrading sewage systems to promoting reef-safe tourism and sustainable development.
And you don’t have to live near a reef to make a difference.
Reefs may be resilient, but they’re not invincible. Every piece of plastic skipped, every cleaner product used, and every advocacy effort adds up. Small changes ripple outward—and those ripples are what coral reefs need most.
