The River Els is the river where Thomas went fishing. The river begins near Ulfstead Castle, before flowing down to meet the River Callan. The nearby town of Elsbridge is named for the bridge that spans the river. From there, the river carries on, running parallel to Thomas' Branch Line until it meets the sea at Knapford Harbour, where two bridges span the river. A canal boat has been seen floating down it. In the television series, The Loop Line crosses the river on a bridge near Elsbridge.