The Muskrat, Musquash or Swamp Beaver Ondatra zibethicus is a large semi aquatic territorial rodent that is native to South America.
It was introduced to Northern Europe and consequently France in the last century as a result of fur farming.
It is now widespread across France inhabiting lakes, ponds and other waterways and causing extensive damage by burrowing into banks. It is considered a pest in France and there are programs to eradicate it.
It grows to a length of about 40 cm and its strong scaly hairless tail is another 20 - 30 cm long.
It weighs in at around 1.7 kg and has partially webbed back feet.
They are extremely good swimmers and are able to stay submerged for up to 15 minutes at a time.
They are crepuscular, meaning they are mainly active in the early mornings and late evenings.
Reference http://www.lost-in-france.com/wildlife-in-france/196-muskrat