Deafeningly loud sonar is a proven danger to marine life, but its use throughout the world's oceans is spreading. This powerful movie, brought to you by the Natural Resources Defense Council and narrated by Pierce Brosnan, shows what sonar does to whales caught within its range, and explains how whales, dolphins and other marine animals can be protected from deadly sonar. www.nrdc.org/wildlife/marine/

This is an older clip, but explains well this still current and dangerous issue. Read about the Navy's new analysis here: switchboard.nrdc.org

"Some systems operate at more than 235 decibels, producing sound waves that can travel across tens or even hundreds of miles of ocean. During testing off the California coast, noise from the Navy's main low-frequency sonar system was detected across the breadth of the northern Pacific Ocean. By the Navy's own estimates, even 300 miles from the source, these sonic waves can retain an intensity of 140 decibels -- a hundred times more intense than the level known to alter the behavior of large whales."

The Navy estimates that there will be 2,000 cases of permanent hearing loss and 1,000 deaths in the next five years due to their upcoming testing. That number does not include temporary hearing loss which often leads to strandings.