From the iconic Battle of Lepanto (1571) to the massive Battle of Leyte Gulf (1944), naval warfare has been a costly and violent aspect of military history. However, a seldom discussed victim of naval wars are the marine ecosystems they disrupt. Unfortunately, our legacy of naval warfare’s impact on marine ecosystems remains devastating with the ongoing full-scale war in Ukraine (2022–present) and the Iran War (2026–present). This article summarises how naval warfare affects marine ecosystems and considers what, if anything, can be done to mitigate the damage.

During the 19th century, naval military drills frequently fired artillery into the ocean. World War I expanded the sources of oceanic pollution through naval mines, air bombs, torpedoes, and depth charges to defend coastlines. Since then, naval war pollution has increased significantly in scale.

In the two decades after World War II, hundreds of thousands of tons of munitions containing chemical agents including mustard gas were dumped into seas around Europe. Explosive munitions such as trinitrotoluene (TNT) and Royal Demolition Explosives (RDX) were also dumped into the Baltic sea. While many of these munitions have not yet exploded, the gradual corrosion of these discarded munitions has caused public health and environmental concerns since the 1950s, when cod catches in areas near the discarded munitions poisoned sea food consumers. In the North Sea, mussels exposed to TNT from ship wrecks of the World Wars have been observed to show less glycogen accumulation in their digestive tissues and decreased detoxification enzyme activity. This means mussels exposed to ship wrecks have a weakened ability to survive periods of low food and to filter water pollution in their habitats.

An even larger crisis is the oil pollution from the thousands of ships sunk in World War II. Out of the 87 shipwrecks within US waters that are considered high priority oil and pollution risks by the National Oceanic and Atmospheric Administration (NOAA) today, 53 were vessels sunk in World War II by Nazi Germany’s U-boats. Military tactics directly worsened environmental impacts, as the German navy deliberately targeted oil cargo ships to prevent American fuel from reaching the British Isles. In the first half of 1942 alone, the Germans sank nearly 580,000 tons of American oil cargo in the Atlantic.

For reference, this fraction of the total oil spilled during World War II exceeds the quantity spilled from the infamous Deepwater Horizon Oil Spill (the largest in US history at 480,000 tons of oil), where an explosion occurred on a drilling site caused years of damage to coastal ecosystems. Thousands of sea turtles, seals, and cetaceans were killed. Additionally, smaller invertebrates such as mussels and mollusks are particularly sensitive to oil, causing their populations to struggle recovering in the oil spill area through the long term .

World War II also included the Pacific War, where allied forces fought the Imperial Japanese Navy. The Pacific War left over 3,800 ship wrecks along the Pacific Ocean. It is estimated that there’s anywhere from 2.5 to 20 million tonnes of oil (across anywhere from 5 to 42 Deepwater Horizon Oil spills) stored within these ship wrecks, depending on how full said ships were at time of sinking. Estimates of corrosion suggest that many of these wrecks are in danger of structural collapse. While gradual leakage is, overall, more probable than sudden catastrophic release, even a gradual release will have damaging impacts on wildlife and habitats. Shipwrecks at higher sea floor elevations are also at higher risk of collapsing and releasing oil due to abundant ocean currents.

An example of real impacts from these sunken vessels was seen in 2001, when the wreck of USS Mississinewa leaked roughly 100 tons of oil into a lagoon of the Federated States of Micronesia, triggering a state of emergency and prohibitions of all fishing in the lagoon. The US Navy spent $6 million USD removing the oil. Additionally, many civilians in the area lost livelihood during the emergency, as fisheries are disproportionately important for civilians on small islands compared to the rest of the world.

It’s worth noting that aquatic habitats are not only affected by naval warfare. During World War II, Imperial Japan killed 80,000 Chinese civilians with chemical weapons. As the war was ending, the Imperial Japanese Army dumped hundreds of thousands of remaining chemical munitions in both soil and water sources. Many of these chemical munitions are soluble in water, making it easy to poison not just soil systems, but lakes and rivers too. The effects of this environmental toxicity were still felt decades post-war, as a 1997 study found over 500 cases of poisoning due to remaining munitions.

The pollution of munitions on land does not just affect the land. Recently, Russia's full scale invasion of Ukraine has produced episodic patterns of pollution pathways, concentrated around rivers and estuaries that flow towards the Northern Black Sea along Odessa Oblast’s coast. The pollutants include residual fuel oil and diesel-esque material. Excess nutrient pollution and lower dissolved oxygen along the coast has also been observed. This is concerning because excess nutrient pollution causes eutrophication, a process in which dissolved oxygen content that marine organisms rely on drops significantly. The damage to natural gradients and borders between fresh and salt water ecosystems during the war has also moved invasive species to new distributions. Thus far, impacts to the Northern Black Sea ecosystem seem recoverable, as much of the biota of the Northern Black Sea is already well adapted to a high pollutant environment, likely minimising the effects of the Ukraine War’s pollution compared to other ecosystems ensnared in war.

Conversely, the Persian Gulf is more fragile and is degrading from ongoing naval and aerial operations in the Iran War. The Persian Gulf’s environment is unique, being a shallow sea largely restricted from the open ocean, with large temperature and salinity extremes. Similar to the Ukraine War, both eutrophication and oil spills are of concern for Persian Gulf ecosystems. Given the small size of Strait of Hormuz, pollutants in the Persian Gulf do not dissipate easily into the wider ocean that can buffer effects of pollution, thus exacerbating damage on the coral reefs and mangroves where diverse fish species raise nurseries. The 1991 Gulf War already gave precedent for the environmental impacts that war can have on the Persian Gulf, where salt marshes and mangroves were devastated by the oil spills associated with the war.

The ecological damage from current and remnants of past wars raise many considerations for future policy, both for the intrinsic value of nature and the ecosystem services that our economies rely on. Suboptimally, we lack much data on the sunken ships in both the Atlantic and Pacific that are at risk of releasing oil, making informed policy difficult. Hull integrity assessments are needed to ascertain the current status of each case to provide a time frame for when oil will be released. Priority cases are currently determined by both the severity and urgency of a ship wreck releasing oil.

In the context of the Persian Gulf, international partners should coordinate monitoring networks to quickly detect large pollutant events and ecological changes. Contingency planning is also required for fragile habitats and vital coastal infrastructure. Long-term ecological damage can cause risk to where industrial cooling and desalination systems are most vulnerable. While resources to protect these ecosystems will be scarce in war time, prior planning could reduce the most extreme damages in a war time scenario.

Regardless of how we restore the environment from our history of war, perhaps the most important takeaway is to avoid any war at all. For both society and nature, there are no winners in wars, only the dead and losers.