Seine Commercial craft (barges and push-tows) can use the river from Marcilly-sur-Seine, to its mouth. At Paris, there are 37 bridges. The river is only above sea level from its mouth, making it slow flowing and thus easily navigable. The Seine Maritime, from the English Channel at Le Havre to Rouen, is the only portion of the Seine used by ocean-going craft. The tidal section of the Seine Maritime is followed by a canalized section ("Basse Seine") with four large multiple locks until the mouth of the Oise at Conflans-Sainte-Honorine (170 km). Smaller locks at Bougival and at Suresnes lift the
Port River of the Barker Inlet and the Port River. Bottlenose dolphins are often seen in the river, examining and following small boats and have become a well known tourist attraction with dolphin cruises departing from "Queens Wharf". The industrialised nature of the Port River has led to concern for the welfare of the bottlenose dolphin population and studies have shown that some of the dolphins have very high heavy metal burdens in comparison to dolphins elsewhere. The mudflats at the mouth of the river are part of the Gulf St Vincent Important Bird Area. Prior to the 1836 settlement of South