The New River is actually a manmade aqueduct dating from the early 17th century, built to bring drinking water into the city and still used for that purpose today.
(Click here for a larger version of the photo above.)
New River Walk is a small park created alongside it in the quiet residential area of Canonbury.
(Click here for a larger version.)
Imagine a peaceful view like this out the back of your house!
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More on the New River Walk at the website of Islington Council, and at Londonist.