Loire

The Loire, at 1,006 kilometers long, is the longest river flowing entirely within France. It rises on the southern slope of Mont Gerbier-de-Jonc in the southeastern Massif Central, in the Ardèche department, and flows into the Atlantic Ocean through an estuary in Loire-Atlantique, in the Pays de la Loire region. Its course initially flows from south to north as far as the vicinity of Briare in the Loiret department, then turns west.
The torrential, narrow-sided Loire initially flows north; from Vorey (Haute-Loire) it tends northeast, then north again from the Grangent reservoir. It generally takes a north-northwest direction from Feurs (Loire), then a distinctly northwesterly one from Digoin (Saône-et-Loire). Between Châteauneuf (Loiret) and Orléans, the boatmen said it was already flowing towards the setting sun, forcing them to navigate against the prevailing wind. From its northernmost point at Orléans, it flows southwest to Candes (Indre-et-Loire) before plunging northwest to Les Ponts-de-Cé (Maine-et-Loire); then west again to the vicinity of Ancenis-Saint-Géréon (Loire-Atlantique), where it resumes its southwesterly course. Between Nantes and Saint-Herblain, it resumes its westward course, gradually descending towards the northwest as far as Saint-Nazaire. It only resumes a final southwest direction at the opening of its maritime estuary.
Its catchment area of ​​117,000 km2 covers more than one-fifth of French territory.
Its course can be described in several successive hydrological basins:

the sub-basin of the upper Loire, up to the bec d'Allier at Cuffy (Cher);
the sub-basin of the middle Loire, from the bec d'Allier to the bec de Vienne at Candes-Saint-Martin (Indre-et-Loire);
the sub-basin of the lower Loire or the lower Loire, from the Vienne confluence to the estuary.
Furthermore, several "regions" can be identified along the river's course. Among these are:

the "Burgundian Loire", from Villerest (Loire) to the bec d'Allier;
the Loire Valley, from Gien (Loiret) to Ingrandes (Maine-et-Loire), classified as a world heritage site from Sully-sur-Loire to Chalonnes (Maine-et-Loire);
the "lower Loire angevine and armoricaine" flowing approximately from Montsoreau (Maine-et-Loire) to Nantes, and crossing the Armorican Massif, which extends from Brittany to the Deux-Sèvres department;
the Loire estuary, where the waters of the Loire and the Atlantic Ocean mix.
Until the mid-19th century, the Loire, navigable from the area around Roanne, was the main waterway for transporting goods from the interior of the country to the port of Nantes. The arrival of the railway, which now connects Paris to Saint-Nazaire via Angers and Le Mans, changed everything. The tidal influence often extends upstream from Nantes, well beyond the wide estuary of Saint-Nazaire. Today, the Loire is navigable from its estuary to Montsoreau (near Saumur).

Source: Wikipedia