Holme Fen is a 269.4-hectare (666-acre) biological Site of Special Scientific Interest near Holme in Huntingdonshire. It is also a National Nature Reserve and a Nature Conservation Review site, Grade I. It is part of the Great Fen project, which aims to create a 3,700-hectare wetland wildlife area including Holme Fen, Woodwalton Fen and other areas. It is home to a variety of birds, including the Eurasian siskin, nightingale and lesser redpoll, and around 450 species of fungi.