The river rises on Mungrisdale Common north of Blencathra and drains much of the eastern and southern sides of the mountain.

The river runs east, then north before sharply turning south at the village of Mungrisdale, skirting almost all around the bottom of Souther Fell.

Latterly, the river turns west to the north of Hutton Moor End and the Trout Beck joins it at Wolt Bridge to the south of Lowside.

The Glenderamackin continues past Threlkeld, at which point it conjoins with St. John's Beck to form the River Greta.

[5] The 'glendera' element is also present in the name of Glenderaterra Beck, which joins the River Greta shortly after its source.