A photo of a line across the sea off Burgh Island shows a natural phenomenon that occurs at the mouth of estuaries. 

Steve Wiltshire took this photo of the sea while he was golfing with his son Beno, 21, on Tuesday lunchtime, 26 March, after spotting the obvious line across the sea. 

He later took to social media to find out what it was. He posted in the Hope Cove Facebook group: "Does anyone know what the strange look of the sea off Burgh Island is all about please?"

The strange line in the sea behind Steve's son Beno

John Brocklebank commented to explain what was happening - he said: "The fresh water is less dense and floats on the salt water. An incoming marine tide will lift up the outgoing fresh water in the mouth of a river. It's called a salt wedge. Mixing will occur at the interface."

Although John said it was "copy and pasted from the internet" so he "couldn't take credit", we're very glad he did because it is a clear explanation for a fascinating effect you can see with your own eyes. 

You learn something new every day.