Upton Fen is a specific location and as such, synonyms for this phrase are difficult to find. However, there are words that are related to the concept of a fen or marshland. Synonyms for the word "fen" might include bog, marsh, swamp, or wetland. These words all describe areas where water covers the surface and plant life thrives. Other related words might include estuary, delta, or floodplain, which all describe areas where a river empties into a larger body of water and creates unique ecosystems. While there may not be direct synonyms for the phrase Upton Fen, these related words can help evoke the sense of a watery, lush landscape.