No it is not a spelling mistake, I am still pursuing some of the lesser-known creatures of the Westcountry, and we are still down on the Somerset Levels (where yesterday I showed you the Pollarded Dryads).
The rhynes are the drainage channels of the Levels. They are the reason why many of the fields have no fences around them: they have their own personal moats instead. When I first came to Somerset I was amazed to see gates standing on the edge of a field with no fence to either side: just a gate, across the entry which was the only point where there was no moat.
They are such a feature of the landscape that over the centuries they have become home to a kind of freshwater mermaid. Very timid, not often seen:
Unfortunately, the pun works better as a visual one: Rhyne is not spelt like Rhine, but like ‘reen’.
There is a little almost-related story I could mention here: I have never swum in any rhynes, they are big ditches and… very pondy… but I have swum in the River Sowy which is an artificial river across the Levels that is exactly like a big rhyne. A little pondy too, if I am honest, but I have swum there now and then. Here it is below, and on my other site, Cat-of-the-Day you can see my drawing of what was an amusingly memorable swim: https://catoftheday.wordpress.com/2014/07/15/a-surprising-tail-15th-july/