You do NOT have to be close to the water to produce that effect around the plane.... It can happen at various altitudes.

It is referred to as the sonic boom cloud. Despite its name, the sonic boom cloud doesn't always come with a sonic boom, and it's not a shock wave of the sound barrier being broken. The clouds only occur in unique weather conditions, when aircraft fly fast enough to cool the air around them, causing moisture in the air to condense into clouds. These halos of vapor appear for only a few seconds when aircraft reach speeds just below or just above the speed of sound (741 miles an hour/1,193 kilometers an hour).




There are cool videos on youtube ....

Excellent explanation......
http://www.youtube.com/watch?v=-d9A2oq1N38