See Derwent-Water Here and Here.

See it on a map Here.

Derwentwater (or Derwent-Water, as Dorothy Wordsworth says), is a body of water in England that Dorothy Wordsworth compares the view of Ben Lomond to. She says that "Up the lake there are no islands; Ben Lomond terminates the view, without any other large mountains; no clouds were upon it, therefore we saw the whole size and form of the mountain, yet it did not appear to me so large as Skiddaw does from Derwent-water" (Wordsworth).

This body of water in England, also known as "Keswick's Lake" comes from the river Derwent and has a long literary history (Visit Cumbria). It is important in literary circles because of Letitia Elizabeth Landon's poem about it in Fisher's Drawing Room Scrap Book, 1837 (Wikipedia).

sources:

https://www.visitcumbria.com/kes/derwentwater/

https://en.wikipedia.org/wiki/Derwentwater