Dry River.

The Dry River or rather the stony bed of it because it was dried out, came from Tumladen and ran benieth the Echoriath to Sirion where the former junktion was near the ford of Brithiac. The tunnel the river once had made benieth the Echoriath had become the secret intrance to Gondolin and Tumladen. The Dry River also divided Dimbar from the Narrow Land.