Parallel sonic worlds: crossfading from above to below water and back

Standing on the river bank watching the boats pass the sound they make underwater is inaudible. However, it is loud and often strident. This recording uses a hydrophone and normal microphones. The track starts above water and slowly crossfades below the surface. Water slopping against the pier is heard from both, albeit differently, but the sound of the boats only underwater. Coots call at the beginning.