Take a microphone and place a windjammer on top of it. The very furry ones do a great job ;)
Then what I did was to record myself rubbing my hand softly on the windjammer just over the microphone membrane. The closer your hand is to the actual microphone the brighter the sound will be.
Then play around and a little EQ’ing and reverb helps a lot!
– Sebastian Stern
Need some ocean and water sounds to get you started? Here’s a selection of ocean sound effects.