Seine

The Seine flows along its entire length through the stratified country of the Paris basin, whose relief is characterized by broad-based high waves, as in the Dry Champagne, and some more concise hills. The narrow valley of the upper course in the plateau of Langres is succeeded in the region of Troyes by a valley bottom about a mile wide between very gentle slopes. Further westwards to the mouth of the Voulzie at Bray-sur-Seine, the valley bottom widens to over 5 km, and finally the slopes become steeper, at least on the north side. The surrounding heights here are about 100 m above the river on the north side, and about 50 m on the south. At Fontainebleau, whose town centre lies in a side valley, there is a valley narrows, in the form of a gate the Seine valley crosses a ridge of heights. At Paris and from there to just before the mouth, the valley runs in numerous loops and correspondingly asymmetrical valley sections with a sliding slope and an impact slope. The width of the valley bottom varies greatly and is narrow for long stretches. The cross-section is asymmetrical even at the Île de la Cité in Paris, where the course of the river is almost straight: south of the river the Quartier Latin does not rise steeply, but nevertheless clearly, while from the north bank the flat Marais ("swamp") extends for several kilometres almost to the Gare du Nord. From Paris to just before the estuary the valley does not become flatter, the valley floor necessarily drops from about 50 m above sea level to near zero, but the elevations remain almost the same.

The Seine valley is known for its numerous castles ("Seine castles"), but also for the automobile industry, petrochemical industry and several power plants located there.

Above the greater Paris area:

• Nogent-sur-Seine: Île Olive, 3 ha

Greater Paris:

• Melun: Île Saint-Étienne, 1200 m × 170 m
• near Évry: Île aux Paveurs, 600 m × 70 m
• Paris:
• Île Saint-Louis, 11 ha, 725 m × 190 m, 2465 inhabitants
• Île de la Cité, 22 ha, 1,19 km × 290 m, 1168 inhabitants
• Île aux Cygnes, 1,3 ha, 890 m × 20 m, uninhabited
• Issy-les-Moulineaux: Île Saint-Germain, 18 ha, parks and residential area
• Boulogne-Billancourt: Île Seguin, 11.5 ha, separated from Île Saint-Germain only by an arm of the river, former Renault factory
• Puteaux: Île de Puteaux, 2,5 km × (140-200) m, recreational area
• Neuilly-sur-Seine and Levallois-Perret: Île de la Grande Jatte, 1,9 km × 150 m, inhabited and recreational area
• L'Île-Saint-Denis: Île Saint-Denis 4,4 km × max. 280 m, 7071 inhabitants
• Carrières-sur-Seine and Chatou: Île de Chatou (Île des Impressionnistes), 8.3 km × max. 280 m
• Louveciennes and Le Port-Marly: Île de la Loge, 2,38 km × (150-220) m
• Andrésy: Île de Nancy, 2.3 km × max. 240 m

Below the Paris metropolitan area

• Near Les Mureaux: Belle-Île, 5.7 km × max. 340 m
• at Mantes-la-Jolie (left bank) and Limay (right bank):
• Île aux Dames: 2,67 km × max. 230 m
• Île l'Aumône: 2 km × max. 278 m
• Bennecourt: Grande Île, 6 km × max 330 m
• Criquebeuf-sur-Seine near Elbeuf: Island with three partial names, Île de Launy - Île de Criquebeuf - Île du Courant, 8.5 km × max. 370 m