Ocean noise pollution is the introduction of human-made sound into the sea at levels that disrupt marine life. The ocean is naturally full of sound, from waves and rain to whale songs and snapping shrimp, but over the past century, industrial activity has dramatically amplified the underwater soundscape. Because sound travels roughly four times faster in water than in air, these noises can affect marine animals across vast distances.
Why Sound Matters Underwater
Marine animals depend on sound the way land animals depend on sight. Whales communicate across hundreds of kilometers using low-frequency calls. Dolphins echolocate to hunt. Fish larvae listen for the sound of a reef to navigate toward it. Crabs, shrimp, and other invertebrates use acoustic cues to find habitat and avoid predators. When human noise floods these channels, it’s the equivalent of trying to have a conversation in a room where someone is running a jackhammer.
Major Sources of Underwater Noise
Commercial shipping is the most widespread source. Tens of thousands of large vessels cross the oceans at any given time, each producing low-frequency noise primarily below 150 Hz that radiates continuously. This hum of global trade forms a constant backdrop of sound across major shipping lanes and port areas.
Seismic surveys used in oil and gas exploration are among the loudest individual sources. Arrays of airguns towed behind vessels release pulses of compressed air at levels between 225 and 250 decibels, firing several times per minute for weeks or months at a stretch. These blasts penetrate the seafloor to map geological formations, but they also propagate through the water column for enormous distances.
Military sonar, particularly mid-frequency active sonar used in submarine detection, produces intense pings that can travel tens of kilometers. Construction of offshore wind farms involves pile driving, where massive steel foundations are hammered into the seabed, generating repeated high-energy impacts. Even smaller vessels like recreational boats and fishing craft contribute, especially in coastal areas where marine life is concentrated.
Effects on Whales and Dolphins
The best-documented harm involves large whales. Shipping noise overlaps directly with the low-frequency calls that baleen whales use to find mates, coordinate feeding, and maintain social bonds. When background noise rises, the effective range of these calls shrinks. A whale that could once be heard 100 kilometers away may only be audible at a fraction of that distance, a problem researchers call “acoustic masking.”
Beyond communication, noise causes measurable physiological stress. A landmark study in the Bay of Fundy, Canada, took advantage of the sudden drop in shipping traffic after September 11, 2001. When large vessel traffic near a right whale conservation area fell from nine ships to three over a matter of days, underwater noise dropped by 6 decibels, with especially significant reductions below 150 Hz. Researchers collecting whale fecal samples found that stress hormone levels decreased in parallel, but only in 2001, not in other years when traffic remained unchanged around the same dates. It was the first direct evidence linking low-frequency shipping noise to chronic stress in whales, with implications for the recovery of the critically endangered North Atlantic right whale population.
Military sonar has been linked to mass strandings of beaked whales, deep-diving species that appear especially vulnerable. Strandings have co-occurred with naval exercises in locations from the Canary Islands to the Mariana Islands in the Western Pacific. The suspected mechanism involves a panic response: startled whales may surface too rapidly, developing something akin to decompression sickness, with gas bubbles forming in their tissues. Establishing definitive cause requires rapid response to strandings, and researchers have called for consistent monitoring networks to investigate what they term “acoustic-barotrauma.”
Harm to Fish and Invertebrates
The damage extends well beyond marine mammals. Laboratory studies on zebrafish embryos show that noise exposure delays hatching, reduces larval heart rates, and increases rates of physical deformity. Nighttime noise proved more harmful than daytime exposure, significantly raising the rate of abnormal development in otoliths, the tiny ear-like structures fish use for balance and orientation. Genes involved in sensory hair cell development were also disrupted. Similar developmental abnormalities have been observed in scallop embryos exposed to noise, suggesting a shared stress response across aquatic species.
For fish larvae drifting in open water, these effects can be critical. Larvae that can’t properly sense their environment may fail to orient toward suitable habitat, reducing their survival. Adult fish exposed to chronic noise show changes in feeding behavior, increased startle responses, and reduced reproductive success. Invertebrates like crabs and lobsters have demonstrated altered movement patterns and reduced foraging efficiency in noisy environments.
How Loud Has the Ocean Become?
Tracking long-term trends in ocean noise is complicated. A recent analysis of acoustic data from nine hydrophones across five oceans, spanning up to 19 consecutive years between 2003 and 2021, found that the majority of monitoring sites actually showed a downward trend in sound pressure levels in the 10 to 100 Hz range. This may seem counterintuitive, but it likely reflects shifts in shipping routes, improvements in vessel design, and the specific locations of monitoring equipment rather than an overall reduction in noise exposure for marine life.
What matters most isn’t a single global average but where and when noise concentrates. Coastal waters, shipping lanes, areas near offshore construction, and regions where seismic surveys are active can experience noise levels far above natural baselines. These are often the same areas where marine animals feed, breed, and raise young.
What’s Being Done
The International Maritime Organization updated its guidelines for reducing underwater noise from shipping in October 2024, with the revised standards taking effect in December of that year. The guidelines provide approaches for ship designers, builders, and operators to reduce what’s called underwater radiated noise through better planning during construction, operation, and vessel modification. They remain voluntary, essentially a framework to raise awareness and encourage adoption rather than a binding regulation.
On the engineering side, one of the most promising strategies targets propeller cavitation, the formation of tiny bubbles on spinning propeller blades that collapse violently and produce significant noise. Researchers at the University of Genoa have demonstrated that custom-designed, optimized propellers can meaningfully reduce radiated noise without sacrificing propulsion efficiency. Full-scale sea trials confirmed the results, suggesting that refitting existing vessels with quieter propellers is a practical option.
Other mitigation tools include bubble curtains around pile-driving sites, which create a wall of air bubbles that absorbs and scatters sound energy before it spreads. Seasonal restrictions on seismic surveys in sensitive areas, speed reductions in shipping lanes near whale habitat, and rerouting vessels away from critical feeding grounds have all shown benefits. Slowing ships down is particularly effective because it reduces both propeller noise and the overall energy of the sound produced.
The challenge is scale. The global shipping fleet numbers roughly 100,000 vessels, and demand for offshore energy, both fossil fuels and wind, continues to grow. Voluntary guidelines help, but many conservation groups argue that binding noise limits, similar to air pollution standards, are needed to drive widespread change.