Shadowy Spring was the shared source of the rivers Esgalduin and Aros which marked the realm of Doriath, located between the Pass of Aglon and Dorthonion.
On the map accompanying The Silmarillion, Christopher Tolkien portrayed the spring of the two rivers as being separate, despite the rivers sharing a common spring on that map which he based his version on, and on a commentary to the first Silmarillion map by his father he admits his portrayal on the published Silmarillion map to be in error. 
- ↑ J.R.R. Tolkien, Christopher Tolkien (ed.), The Lost Road and Other Writings, "Appendix: III. The Second 'Silmarillion' Map" p. 409
J.R.R. Tolkien, Christopher Tolkien (ed.), The Shaping of Middle-earth, "IV. The First 'Silmarillion' Map: The Northern Half of the Map" p. 222