Pile driving at large construction sites produces formidable noise. Marine pile driving similarly can produce high sound pressures underwaterâ€but these can be lethal to fish and can harass marine mammals, including those protected by federal law. This problem has contributed to costly construction delays on major bridge projects. To protect marine life, engineers have designed air bubble curtains to reduce underwater sounds. Air provides an effective barrier to sound propagating through water, because of the difference in density between air and water. Air bubble curtain systems have been used to reduce underwater sound pressures from explosions or from other sources of high-amplitude sounds.