Originally called Glinduin (S. "River of Song") this river formed the boundary between Lebennin and Dor-en-Ernil. Though it broadened into an estuary below its confluence with the Serni, the Glinduin was unnavigable within a mile above Linhir. At this point, its swift-flowing stream meandered into a broad and shallow mere,the Ael Glinduin which terminated in a waterfall as it narrowed once again to continue its journey to the sea. It was the constant noise of this low waterfall which gave the river its name. The swiftness of the river above the mere prevented a safe fording, except at one spot, thirty miles upstream, where its banks widened enough to permit passage.The river was bridged at the town of Linhir. seven miles below the falls.
In T.A. 1981, the River Glinduin was renamed Gilrain (S. "Wandering Srar"), in memory of the lost Elven maiden Nimrodel whom, it was said, found respite beside the waters of the mere, recalling the beloved stream of her homeland. The story told that, weary from her long and fruitless search to be reunited with her lost Amroth, Nimrodel fell into a dark sleep beside the mere. Mithrellas, her handmaid, continued to seek Edhellond, but fate decreed that she should find instead Prince Imrazôr of Dol Amroth and having told him of her mistress' misfortune, would lead the Dúnadan back to the mere. But when they came to that place, Nimrodel was gone, and none marked what doom had taken her.
- MERP:Southern Gondor - The Land