When a gust of wind touches the surface of calm water, it creates a localised patch of bigger ripples. These can be seen as a different colour, normally darker. The effect has the nickname ‘cat’s paws’ as some people believe it looks like a cat’s paw print or a cat scratching at the surface of the water.
For dinghy sailors and others on the water, there is no technology and possibly never will be that can predict the arrival of a gust of wind as effectively as cat’s paws.
In this photo of Arlington Reservoir, the wind is blowing away from us and we can clearly see the darker patches – the cat’s paws – giving us a great map of where the strong gusts of wind are.