The Seine River is a total of 776 kilometers (482 miles) long, and flows from Source-Seine near Dijon to Le Havre and into the English Channel. From Le Havre, almost 120 kilometers (75 miles) of the Seine River is still navigable by large ships that sail the oceans. Almost the entire length of the Seine is navigable by regular-sized riverboats, and recreational boats can be found across the entire length of the River.
In Paris, the Seine used to be a shallow river with sandy banks. However, over the years locks were installed to raise the water level, and nowadays there are no natural sandy banks left in the city. The river depth is also tightly controlled, and averages 9½ meters (31 feet). Nonetheless, the Seine has flooded Paris on numerous occasions, some even recently. For example, in 2003 the water level rose so quickly that about 100,000 works of art, which were stored underground, were moved out of the city. Paris hadn’t seen a relocation of art of this scale since the Second World War.
More on The Seine: http://www.nyhabitat.com/blog/2012/09/13/seine-river-paris/