The Tenneril River

The Tenneril River flows south, from somewhere deep in the continent of Chadun, along the western edge of the Forges. There it widens into a lake called Aven Crum, from which a smaller branch of the Tenneril continues to flow southward towards the Malfa peninsula.
Originally, the river then petered out into swampy lowlands at the base of the peninsula. A couple of centuries ago, a pact between the Maveren and the Hewellen resulted in a massive magical working called The Deeping, which collected the water lowlands into a river so that it reached all the way to the town of Malfa and its port. This is what gave Malfa the main trade access to the interior of southern Chadun.
North of Malfa, various peoples live along the banks of the Tenneril, mostly humans and river dwarves. Further north that that, there are rumours of massive forests and/or insular kingdoms, at the headwaters of the Tenneril.
The branch of the Tenneril that extends to Malfa is called the Sluice, a name originally given it by the Hewellen. The tributary that comes down from the Forges to meet the river at Aven Crum is called the Sliver. It flows partly below ground, and is just barely navigable enough for trade with the Hewellen settlements in the mountains.