Ferries and other craft crossing Sydney Harbour naturally leave a distinct wake, signified by trails of a lighter colour than the surrounding water. These sometimes persist for more than 30 minutes after the craft has passed through, and the surface takes on an appearance reminiscent of ski trails through virgin snow. How can this be so on a body of water that is in constant, albeit gentle, motion?
Barry Clendinning, Manly, New South Wales, Australia
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