Oil Spills: The impact on the marine environment - Riskaware

Oil Spills: The impact on the marine environment

“ITOPF estimated that between 1970 and 2023 approximately 3.7 million tonnes of oil were spilt into the ocean, with 1.5 million of this due to large tanker oil spills (7 tonnes and above), each having a profound impact on the marine environment”

Our World in Data  

The general global trend shows tanker oil spill incidents on the decline, decreasing by over 90% between 1970 and 2010s to an average of 6.3 per year. Nevertheless, oil spills of any size have a significant impact on the marine environment, however infrequent they may now be.

In 2022, the ITOPF recorded three large spills (greater than 700 tonnes) and four medium spills (7 to 700 tonnes) from tankers globally. And smaller oil spills are still an extremely prevalent threat which are not recorded to the same degree. Most of these are caused by collisions/allisions or groundings. 

Additionally, not all oil spills come from tankers. These statistics only show part of the picture, with other spills not accounted for coming from incidents like the Deepwater Horizon oil rig explosion 

So, despite the positive trend that vessel spills are becoming less common, the scale of the potential impacts from even one spill shouldn’t be overlooked.  

What are the causes of oil spills into the ocean?

Oil spills can occur naturally, through oil leakage points or “seeps”. This is when crude oil enters water bodies through cracks or fractures in the ocean floor.  

But, due to the relatively small amount of oil released, these natural sources are not nearly as impactful on the marine environment and our coastlines as oil spill incidents caused by humans. Two of the primary contributors to oil-related incidents are wellhead blowouts, such as the Deepwater Horizon disaster, and tanker spills, like the Exxon Valdez.  

Although events caused by human activity may be relatively less frequent than natural oil leakage, they can have much more widespread and dramatic consequences. 

What are the potential effects of oil spills?

Oil spills can have a profound and devastating impact on the marine environment. Many of these environmental impacts will permeate long after the spill incident itself has occurred.  

Many consequences can be felt immediately – such as oil soaking wildlife and coastlines – but many are equally insidious and complex – such as the direct and indirect influences on the economy and public health long-term.  


Both marine and land habitats and animal populations can be affected by an oil spill. Birds, fish, and other sea life can be harmed if not killed by oil. For example, they may be coated in oil, which impacts their ability to move, thermoregulate and eat, or become trapped in oil slicks completely.  

These impacts on wildlife can be seen long after an oil spill, in some cases even affecting the new generation of the population.  


Oil spills can impact marine ecosystems, such as oceans, coastlines, rivers, seabeds and more. Oil has the potential to destroy habitats, particularly sensitive or protected area, such as mangroves or coral reefs. They will likely disrupt the natural ecosystems that make up these environments.  


From fishing industries to agriculture, the local business economy may feel the effects of both physical damage and limitations for many years after an oil spill. Many people could lose their income and/or their livelihoods.  

Whilst fines placed on the parties responsible can help compensate governments and local communities impacted by a spill, they are unlikely to cover the large immediate cost to the economy.  


Tourist destinations, and therefore businesses that take advantage of these areas, are often directly impacted by oil spills as a consequence of oil washing up on beaches or hitting the coast. There is also a more intangible affect as global perceptions of said destination can negatively shift after such an event.


Local communities will be affected by all of the impacts outlines above. It can influence their lifestyles and way of working for many years. For example, impacts on fisheries can affect both food production for a population as well as economic positions. Populations in proximity to the spill may also experience health impacts through direct exposure to the oil, or secondary impacts such as air pollution.

How emergency services plan oil spill response

Real-world examples of oil spills and their impact on the marine environment 

Exxon Valdez

On 23rd March 1989 the Valdez oil tanker struck Bligh Reef in Prince William Sound, Alaska. More than 11 million gallons of crude oil were spilled causing devastation across thousands of miles. This spill is estimated to be one of the more expensive in history and still, 20 years later, the oil not removed continues to be a problem.

Key impacts:

  • Wildlife: It’s estimated that 250,000 seabirds, 2,800 sea otters, 300 harbour seals, 250 bald eagles and up to 22 killer whales were killed. 25 years after the spill, several species still hadn’t recovered.  
  • Environment: Over 1,300 miles of shoreline were affected by the oil and it’s estimated that 16,000 gallons were still present in the waters of Prince William Sound as of 2020. Clean-up teams working on the Exxon Valdez spill have estimated that shoreline habitats, such as mussel beds, which have been affected were predicted to take decades to recover fully.  
  • Economy: The local fishing industry experienced over $300 million in economic harm and clean-up costs reached around $2 billion, with total economic loss estimated at roughly $2.8 billion.  
  • Tourism: Tourism-related spending decreased by 8 percent in south-central Alaska and by 35 percent in southwest Alaska in the year after the spill.  

Deepwater Horizon

Deepwater Horizon remains the largest oil spill in US history. Taking place off the Gulf of Mexico on 10th April 2020, the oil rig explosion released 134 million gallons of oil into the water.

  • Wildlife: It was estimated that 21 species of dolphins and whales have demonstrable injuries. The dolphin population in certain areas was predicted to decline by half, taking over one hundred years to recover.  
  • Environment: In 2015, five years after the spills, it was confirmed that at least 770 square miles of Gulf floor were affected, and the habitats could take decades to hundreds of years to recover.  
  • Tourism: Hotel cancellations throughout the Gulf Coast rose to 35% 2 weeks after the spill, and reached 60% after 6 weeks, with total leisure visitor spending dropping by $247 million in the year of the disaster 


The FSO Safer is a floating oil tanker located in the Red Sea off the Yemeni coast which was at risk of spilling tonnes of oil through a leak or an explosion. Due to degradation, this situation became a global concern and the amount of oil spilled had the potential to be 4x larger than the Exxon Valdez.  

After years of operational planning, the more than 1.1 million barrels of oil were safely removed from the tanker in 2023 

Download our full case study on FSO SAFER

Potential impacts modelled by Riskaware in 2020:  

  • Environment: Water and coastline contamination could have extended to the Bab-el-Mandeb strait and the Gulf of Aden. In the event of a fire 40% of agricultural land would have been covered in deposits from the smoke.  
  • Economy: 100% of fisheries were at risk of being impacted, ports would close, and $70 million could be lost in agriculture production. Fuel prices would resultantly spike due to the closure of ports, and the fish stock could take over 25 years to recover, altogether increasing the need for humanitarian aid and food aid significantly. The overall costs of oil spill cleanup could have reached $20 billion.  
  • People: A fire onboard the FSO Safer could have exposed over 8 million people to air pollution from the resulting smoke plumes, alongside the potential for contaminated water supplies from an oil spill. Roughly 4 million people, including fishermen and farmers, would have lost their livelihoods causing mass moves inland.  


On 6th January 2018, the Sanchi tanker collided with the CF Crystal carrier off Shanghai. The tanker was breached and burned for over a week before sinking.  

Key impacts:  

  • People: 32 crew members onboard the Sanchi were presumed perished in the disaster.  
  • Environment: Ultimately, the spill created four oil slicks which covered 100 square km of ocean. Due to the fire, carcinogenic fumes were likely to pollute surrounding islands, reefs and other coastal areas as well as the air quality in the area.  
  • Wildlife: The slick passed through the migratory paths of the humpback while and sea turtles. 

How can oil spill impacts be avoided? 

Time is of the essence in these situations. The longer the oil is in the water, the further it will spread and the more deeply the consequences will be felt. In some incidents oil has been found for years after the initial event, continuing to cost money and degrade environments during this time. Impacts often permeate for decades more.  

Preventing any further spillage, as well as containing and cleaning up the oil that has been spilled, is imperative for minimising these impacts. In particular, safeguarding the nearby coasts and land will often be a priority for responders as impacts to these areas can be some of the most severe.  

Oil spill models, such as the one developed by Riskaware, can help reduce the environmental, economic, and humanitarian impact of a spill. These models can predict the oil’s trajectory on the surface of the water, allowing response teams to direct their activity and attempt to mitigate the spread in a targeted way.  

As an incident progresses, modelling can also show the potential impacts on other marine environments such as the shoreline. This helps to focus and optimise clean-up operations.   

A huge benefit of this technique is that it can be employed before regular surveillance operations, for a faster and more informed response.  

Learn more about the emergence of oil spill modelling for effective response  

Download our MarineAware brochure or view our case studies for more information about our oil spill modelling solution. 

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