Only eight rivers run through the North York Moors. Of those, all but two eventually drain into the Ouse, and then the Humber. Of those two, although the Leven rises in the moors, it quickly drops down onto the plains around Great Ayton and for most of its length is a lowland river, eventually joining the Tees.
The most peculiar of these rivers is the Derwent. This rises on the high moors overlooking the North Sea, flows south through the moors, and then cuts its way through Forge Valley onto the vale of Pickering, close to Scarborough. At this point it is only four miles from the sea at Scarborough, but instead of flowing east to the sea, the Derwent turns right and flows west and then south for fifty miles, joining the Ouse near Goole. On its way it gathers up the waters of the five rivers of the western moors - the Rye, Seph, Riccal, Dove and Seven. This unusual route to the sea only came about at the end of the last ice age, when melt waters from the great glaciers that covered the north sea overflowed the top of the Tabular Hills, cutting a new route south. Before that, the upper Derwent did indeed flow east, reaching the sea north of Scarborough. A portion of its waters still do, diverted from their normal course along the Sea Cut.
Only the Rye, Riccal and Esk give their names to the dales they flow through. The Seph flows through Bilsdale, the Dove out of Farndale and the Seven out of Rosedale. The Esk is unique amongst the Moorland rivers in that it rises in the moors, flows west to east through them, and reaches the sea (at Whitby). The result is to give Esk Dale a rather different feel to the other Moorland dales.