Dwarvensluice
The Dwarvensluice is a major waterway in the Fallow Marches, connecting Tinker Hall and Tamwood Fork on the Castella River. The 'Sluice is one hundred and fifty miles long, and almost universally one hundred and twenty feet across. The Dwarven engineers and Earth mages have put a lot of effort into the river, and while the west bank is mostly wild, the east is stone reinforced with a commercial towpath atop the embankment.
The Dwarvensluice is the primary overland trade route out of Tinker Hall, and the main output for the numerous underground streams that emerge from the mountain. Worked goods, beer, and bulk grain for Tamwood Forkcome down the river, while logs and Asterian trade goods go up.
There does not appear to be a manifest elemental spirit associated with this waterway. If asked, Castella with mention that there used to be a drake that ruled it, millennia ago, but the Tinker Dwarves' animosity towards dragon-kin is legendary.