From its source on Dartmoor it flows in a generally southerly direction past some of the best-preserved archaeological remains on the moor.

It leaves the moor at the town of Ivybridge and continues southward, passing the settlements of Ermington, Modbury and Holbeton.

Most of these have not been positively identified, but the name Aramis/Aranus/Armis was suggested to be the River Erme by Rivet and Smith in The Place-names of Roman Britain (1979).

Between these two sources lies Duck's Pool, where there is a plaque and letterbox in memory of the Dartmoor author William Crossing.

There are extensive early tin mining workings nearby known as Erme Pits, which are in places over 15 metres deep.

The confluence of Red Lake, and the source of the Erme are two of the thirty-three places that delineate the ancient boundary of the Forest of Dartmoor.

On this stretch, a short stream flowing down Hortonsford Bottom from Langcombe Hill also joins the river from the south.

Between Stingers Hill and Redlake the river turns southward into an area known as The Meadow, where it is crossed by the Upper Erme stone row, the longest on Dartmoor at 3,320 m (10,890 ft).

[6] For the next mile or more downstream from here there are extensive archaeological remains on the river's banks, most notably Erme Pound (the highest and largest Bronze Age enclosure in the area),[7] Downing's House (a well-preserved "tinner's cache" or "beehive hut" with much of its roof preserved),[8] and a number of tinner's huts and blowing houses.

As the river reaches the edge of the high moor, it flows through the gorge it has cut between Stalldown Barrow on the west and Piles Hill to the east.

Here, on the eastern bank, lies Piles Copse which is one of the few areas of ancient woodland on Dartmoor and a Site of Special Scientific Interest.

[9] Leaving the open moor, the river passes into enclosed land and under its first road bridge at the hamlet of Harford.

From Harford down to the boundary of the national park, which here follows the main railway line between Plymouth and Exeter, much of the river's course is in woodland and is a popular site for kayaking and canoeing, especially in Long Timber Woods.

Immediately south of Ivybridge, the river passes beneath the A38 Devon Expressway – the main road link between Exeter and Plymouth – and then continues to flow southerly through countryside.

[13] As it passes to the east of the village of Holbeton the Erme becomes a ria with extensive areas of salt marsh and mud that are uncovered at low tide.

From Clyng Corn Mill (now a private house to Orcheton Quay) there used to be a canal which has long since silted up and is now just a small stream.

At the court martial, the vessel's pilot stated that he believed that he was entering Plymouth Sound, some 14 miles west.

[30] There was a memory of a dog setting off mines on the estuary recorded in a publication produced by the Kingston History Society.

The 1919 and 1947 Ordnance Survey maps show a "rifle range" stretching up the estuary from Owen's Point to Pamflete—this may have been related to war time activity.

In 1985 Scobbiscombe Farm, which is above and just to the east of the estuary, was used as a location for the film Revolution which concerned the American War of Independence.

The cast included Al Pacino, Donald Sutherland and a whole host of cut out British Red Coats, one of whom found a new home in a local greenhouse for a while.