River Helvander

The River Helvander is a major river running for over a thousand miles through the eastern half of Rhydain, following a generally southwest-to-northeast course from its headwaters in mountainous Rhyndara and Tholomyra to its mouth on the Modrinian coast, where it empties into Orphan-Bird's Bay (a part of the Sea of Tyrus). Along its northern edge, the drainage basin of the Helvander is defined by the might Adhemars; its southern boundary is formed by the Helgremars, the Lokenmoor, and the northwestern flanks of the Tythian Massif. 
The Helvander is generally held to be divided into upper and lower courses by the Helvander Cataracts, just upstream of the major river-port of Torrune. The lower Helvander is the part of the river which lies below them, and the upper is that which lies above. However, the stretch of river from the cataracts down to Temsevar is sometimes called the 'middle' rather than 'lower' Helvander, with only that portion below Temsevar (i.e. the portion that flows through Modrinia) being considered the true lower river. 
The Helvander and its valley (the middle and lower parts of which are called the Helvanderûn) form the main route of trade and travel through eastern Rhydain, and most of the region’s major towns and cities are situated along it. It is the backbone and namesake of the Helvandrian League, and the heartland of the larger region known as the Taefemach.
Major tributaries of the Helvander include the XXXXX, XXXXXX, XXXXX, and XXXXX flowing down from the Adhemars to the north; the XXXX and XXXXX flowing from the Helgremars of Rhyndara; the Greywine and XXXXX arising in the highlands of the Lokenmoor; the XXXXXX and XXXXX running down from the west flank of the Tythian Massif; and the XXXXXXX rushing down into Modrinia from the Mountains of the Morn.