Slick lines form on water when a very thin layer of oil spreads out across the water. The oil dampens ripples creating calmer patches.
Over time, the wind corrals these patches into long thin lines. The photo above shows a small scale one, but they can spread for many miles. This one is likely from a drop of oil from a boat engine, but many are caused by natural oils, in seaweeds or marine life.
From the book, How to Read Water:
“Any oil spreading across an area of rippled water will be clearly visible as a series of lighter areas. The reason that water with oil on it appears lighter in colour than the surrounding water is because the ripples have been flattened out, which means that more of the sky gets reflected.”
How to Read Water by Tristan Gooley
One of the most interesting things about the image above is that the slick line is clearly visible in a small darker patch of water. Regular water readers will recognise this as a sign of a gust of wind known as a Cat’s Paw.
There is another example of a slick line, this time on a greater scale, on this page.
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