It is of earlier origin than Venice, and indeed is probably identical with the Roman Portus Aedro, or Ebro, though its name is derived from the Roman Fossa Claudia, a canalized estuary which with the two mouths of the Meduacus (Brenta) went to form the harbour.
Between 1892 and 1899 the river was canalized along its right bank for a distance of 43 m.
The southern branch turns south, crosses the marsh of Biesbosch by the canalized channel of New Merwede, enters the Hollandsch Diep, and reaches the sea by the arms called Haringvliet and Krammer.
In Belgium it is canalized between Liege and Vise, and the Dutch are engaged on the same operation below Maestricht.
Amsterdam, the "dam or dyke of the Amstel," is so called from the Amstel, the canalized river which passes through the city to the Y.