A bubble curtain is a wall of air bubbles rising from the bottom of a body of water, created by pumping compressed air through perforated pipes or hoses laid along the seafloor, lakebed, or riverbed. It acts as an underwater barrier that can block sound, redirect fish, contain debris, or add oxygen to the water. Though the concept is simple, bubble curtains have become a critical tool in offshore construction, environmental protection, and water management.
How a Bubble Curtain Works
The basic setup involves an air compressor connected to a length of pipe or hose with small holes drilled at regular intervals. When the compressor runs, air is forced through those holes and escapes as a dense stream of bubbles that rises to the surface. The rising bubbles drag water upward with them, creating a vertical current and a continuous “curtain” that stretches the full length of the pipe.
The size and spacing of the holes, the air pressure, and the depth of the water all affect how dense and effective the curtain is. Some installations use multiple parallel pipes and several large compressors to create a thicker, more consistent barrier. In offshore wind farm construction, for example, a perforated hose is typically arranged in a wide ring on the seabed around a work site, forming a circular wall of bubbles that can be 180 meters across.
Reducing Underwater Noise
The most high-profile use of bubble curtains today is noise reduction during offshore construction, particularly when steel piles are hammered into the seabed to anchor wind turbines. Impact pile driving generates intense underwater sound waves that can travel enormous distances and harm marine mammals. A bubble curtain surrounding the pile site disrupts those sound waves as they pass through, because each bubble acts as a tiny pocket of air that absorbs and scatters acoustic energy.
The results are significant. Measurements from double big bubble curtain systems show noise reductions of 14 to 17 decibels at 750 meters from the pile, according to research published in Frontiers in Marine Science. At 1,500 meters, the reduction still holds at 14 to 15 decibels. Because the decibel scale is logarithmic, a 15-decibel reduction means the sound intensity reaching marine animals is roughly 30 times lower than it would be without the curtain.
In April 2025, RWE deployed bubble curtain technology at the Sofia Offshore Wind Farm, located 195 kilometers off England’s coast in a protected zone for harbour porpoises. It was the first use of the technology for offshore wind construction in the UK, though bubble curtains have been standard practice across European wind farms for years. The deployment aligns with updated UK government guidance on reducing underwater noise from offshore construction, issued by DEFRA in January 2025.
Protecting Marine Wildlife
Bubble curtains aren’t just a nice-to-have. In many cases, regulators require them. The U.S. Navy, for example, is required to use bubble curtains during impact driving of steel piles in Puget Sound, Washington, where construction activities could affect up to 10 species of marine mammals, including gray whales, humpback whales, killer whales, harbour porpoises, and several species of seals and sea lions. The National Oceanic and Atmospheric Administration issues incidental harassment authorizations for these projects, and bubble curtains are a key condition for approval.
The requirement typically applies to steel pile driving specifically, since that generates the loudest underwater noise. Other pile types with lower source levels often don’t require curtains, partly because deploying the system at every pile location slows down construction considerably.
Guiding Fish Away From Danger
Beyond noise, bubble curtains serve as behavioral barriers for fish. The wall of rising bubbles creates a visible, audible, and physical disturbance in the water that many fish species instinctively avoid. Experimental research on fish guidance systems has found that bubble curtains produce a significant velocity gradient near the curtain, which changes the local water flow enough to deter fish from crossing into dangerous areas like water intake pipes or hydroelectric turbines.
This application has been used at power plants, water treatment facilities, and dams. The curtain doesn’t physically block fish the way a net would. Instead, it exploits their natural tendency to avoid unfamiliar turbulence and noise. Effectiveness varies by species, water conditions, and how the system is configured, but bubble curtains remain one of the simplest non-physical fish deterrents available.
Improving Water Quality
In lakes, ponds, and reservoirs, bubble curtains serve a different purpose: aeration. As bubbles rise through the water column, they transfer oxygen from the air into the surrounding water and create circulation that mixes oxygen-poor bottom layers with oxygen-rich surface layers. This can prevent the stagnant, low-oxygen conditions at the bottom of a lake that lead to fish kills, foul odors, and the release of phosphorus from sediment (which fuels harmful algal blooms).
There are tradeoffs, though. Small bubble aeration systems can disrupt a water body’s natural temperature layers. In one case involving a fish-rearing pond in Virginia, a small bubble system raised bottom water temperatures by about 5°C in just five days, roughly ten times faster than the natural warming rate. That kind of thermal disruption can be dangerous for temperature-sensitive species. More advanced oxygenation systems have been developed to add dissolved oxygen without mixing warm and cold layers, but traditional bubble curtain aeration remains widely used in situations where thermal stratification is less critical.
Containing Surface Debris
Bubble curtains have also been tested as barriers to trap floating plastic and other debris in rivers and canals. The concept is straightforward: a curtain of bubbles angled across a waterway pushes floating material toward a collection point on the surface, where it can be removed. Several pilot projects in European waterways have used this approach to intercept plastic waste before it reaches the ocean. The rising current created by the bubbles nudges lightweight debris upward and to one side while allowing fish, boats, and water to pass through freely. This makes bubble curtains appealing for urban waterways where a physical barrier would block navigation.
Limitations and Practical Considerations
Bubble curtains are not a perfect solution for every situation. Strong currents can push bubbles sideways and create gaps in the barrier. Deep water requires more air pressure, which means bigger compressors and higher energy costs. In offshore settings, deploying and retrieving the hose system at each new pile location adds time to construction schedules, which is why operators sometimes skip the curtain for quieter pile types.
Environmental conditions matter too. Wave action, tidal changes, and water depth all affect how uniformly the bubbles rise and how effectively they block sound or redirect fish. Double bubble curtain systems, which use two concentric rings of hose, generally outperform single curtains but cost more to install and operate. Engineers typically model the specific site conditions before choosing a configuration, balancing noise reduction targets against practical constraints like water depth, current speed, and the sensitivity of nearby wildlife populations.