Why can dolphins be heard for miles below water but not above?

Dolphins can be heard for miles underwater due to the efficient transmission of sound in water, which is denser than air and allows sound waves to travel farther and with less attenuation. Their vocalizations, including clicks and whistles, are adapted to this medium, enabling effective communication over long distances. In contrast, sound dissipates more quickly in air, making it difficult for their calls to be heard above water. Additionally, the frequency of dolphin sounds is often optimized for underwater transmission, further limiting their audibility in the air.