It connects by a short section of river to the Loch of the Lowes, immediately to the south.

The loch takes its name from a church dedicated to St Mary which once stood on its northern shore, although only the burial ground is now visible.

[2] As the loch is sheltered by steep hills on all sides it is often very still, providing excellent reflections in its waters.

The Southern Upland Way and Sir Walter Scott Way long-distance walking routes both pass the shores of the loch.

[5] Many of the 71 Noctes Ambrosianae in Blackwood's Magazine refer to Tibbie Shiel's Inn and St Mary's Loch.