Watermill Cove is located on the northeast side of St Mary’s Island, the largest island of Scilly. It offers an anchorage in a remote location just off one of the primary routes into the island group.

Watermill Cove is well sheltered from south round through west to northwest. It is a key anchorage as it is one of the best places in the group to endure the winds of a southwesterly gale albeit not in comfort as a heavy southwesterly swell tends to wrap around the island and make its way into the cove. The bay needs attentive navigation in daylight as although approaches from seaward are open some care is required to anchor clear of fringing ledges and a rocky outlier.

Keyfacts for Watermill Cove

Position and approaches

Haven position

49° 55.960' N, 006° 17.147' W

This is on the 3-metre contour in the northwest corner of the bay.

What is the initial fix?

This is on the 10-metre contour aligning an approach between the ledge extending from Black House Point and the rock awash in the centre of the bay.

What are the key points of the approach?

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What's the story here?

Watermill Cove is a historic anchorage in a remote setting on the northwest coast of St Mary's Island, Isles of Scilly. It presents a beautiful sandy beach fronted by clear blue water at low water. It is a remote location well used by passing yachts as it provides both a good anchorage and a tide wait location laying adjacent to Crow Sound, which requires sufficient rise of the tide to pass over Crow Bar, 1 metre LAT.



The anchorage is in the northwest end of the bay as the expanse of water in the middle and south-eastern part of the bay, known as Tregear's Porth, is made unusable by rocky ledges. These extend out as far as the local small boat moorings and it remains shallow out for a further 100 metres. The anchoring area is in the northwest side of the bay entered between a covered rock and a ledge extending from Black House Point. It has ample depths but the further a vessel can proceed in the better the protection it offers.

How to get in?

Use southwestern England’s coastal overview for Land's End to Isles of Scilly . Located on the northeastern side of the island group the wide entrance of Crow Sound that lies between St Mary's and the Eastern Isles along with St Martin's is not difficult to identify. It is 1 mile wide at its narrowest which is between Tolls Island and the small Biggal Rock which is 1 metre high and located 300 metres to south by southeast of Great Arthur. Standing out 200 metres from the coast clears all the dangers on St Mary’s between Toll’s Island and Innisidgen.




The western end of Crow Sound is partially enclosed by Hats. This is a shoal that dries to 0.6 metres and an uncovering boiler structure from a wreck in the sound. It is marked by the 'Hats' south cardinal marker, VQ(6)+LF1.10s, moored 400 metres southward of the boiler and the same distance east northeast of Innisidgen.




The 'Hats' south cardinal marker provides a helpful mark to identify the bay as the anchoring location is located about a ¼ of a mile southward of the buoy. Except at high water springs, when it covers, the sandy beach should stand out on the shoreline. Black House Point, overlooking the western side of the bay, is made prominent by a sweep of pine trees on the crest of the hill.




The primary danger when anchoring in the northwest side of the bay is a rock shelf extending from Black House Point and a central rock just awash at LAT. Stand well off Black House Point as the shelf, that dries to 1.3 metres, extends almost 200 metres east by northeast from the point. The rock awash is situated well to seaward and in the centre of the cove, out about 100 metres to seaward of a line joining its two headlands. The anchorage is approached between this rock and the ledge extending out from Black House Point.




The initial fix is on the 10-metre contour just outside these two dangers in the northwest end of the bay. Start sounding in for a distance of 150 metres towards the beach at the head of the cove - if it is exposed and visible.




This should represent a south-westerly bearing of about 215° T. If there is any uncertainty Carn Wethers, the bluff headland on the eastern extremity of St Martin’s kept just open to the east of the hump of Great Ganinick island, provides a back bearing that can confirm the safe line of approach into the anchorage. Likewise, keeping the north end of Innisidgen just open of the rocky islet just off Black House Point will provide depths of between 3 to 5 metres LAT. After this, it shallows rapidly.




Anchor over a mostly sand and weed bottom with some small rounded boulders that provide moderately good holding. Make certain that there is adequate swing room and if there is any concern it is worth putting out a second and Bahamian moor.




Land by dinghy on Watermill Cove's fine sandy beach. A footpath leads up from the beach to a lane leading to the island's main roadways. It is also possible to land at Tregear's Porth which has a low tide approach channel dug out from the sand. It is the ideal place to land for those heading over the hill to Pelistry Bay.

Why visit here?

The first settlers of Scilly were Neolithic, but a more comprehensive settlement of the islands came in the Bronze Age, up to 4000 years ago. They left as many as 80 prehistoric chambered tombs or entrance graves around the isles and two of the best-preserved lie at Innisidgen a quarter of a mile northwest of the anchorage.




Located just above the root of Innisidgen Islet there is an upper and a lower chamber. The name 'entrance grave' can be misleading as it is believed unlikely that such splendid ritual standing stones and stoutly constructed burial chambers were constructed solely for burial purposes. Although nothing was found within them when they were excavated, in 1854, the walls revealed traces of rough clay mortar that suggested it was once plastered and possibly even decorated. This would suggest that the 'graves' could also have functioned as shrines or as a focus of ceremonies.




Watermill Cove has its legacy of historic structures albeit more difficult to identify. This island corner was heavily fortified during the English Civil War from 1642 to 1651 on Scilly. Its strategic position at the entrance to Crow Sound and the sheltered landing places of its old quay at Tregear's Porth and Pelistry Bay beach made it vulnerable to an invading army. Gun batteries were mounted on the crest and northern slope of the spur between Tregear's Porth and Pelistry Bay bringing any vessel entering Crow Sound well within range. Breastworks were also along the southeast coast-facing slope of Pelistry Bay along the western side of Watermill Cove.

The quay at Tregear's Porth continued in use until the 18th century, for the export of kelp ash. This was the product of burning seaweed in pits that were on Toll's Island to extract the large proportion of iodine that kelp contains. The ash was used initially in the production of glass, and it was also mixed with animal fats and was then widely used as an antiseptic and ointment for cuts and sores - see Tean where kelp burning was introduced into the island group.

Today the remains of the old quay is still visible and the slipway serves small open boats that moor on the east side of the cove. The fortifications, less so, as unlike The Garrison’s breastworks and batteries that were retained and repaired in 1715, very few of these defences survived elsewhere on the island. This has left Watermill Cove as a quiet remote and little-developed location with clear blue water and a beautiful sandy beach. The coastal footpath meanders past the impressive Innisidgen Bronze Age burial cairns on its way around to Hugh Town a shortcut can be taken across the island but it is less enjoyable than the coastal path. To the east, the pathway leads to the fine beach at Pelistry Bay where you can walk at low tide, 'Famous Five' style, across to Toll’s Island for a mini-adventure. Just be aware swimming is dangerous here on account of strong tides and rips.




From a boating point of view, the historic anchorage is as important as today as it was to mariners in the past. Adjacent to one of the two main eastern entry channels into St Mary's Road, Watermill Cove is an ideal location to wait for a sufficient rise of tide over Crow Bar (least depth 1 metre). Likewise, for those on St Mary’s Pool, once the westerlies freshen and start to turn northwest a quick circuit around the island, via Crow Sound or a little longer at low water by St Mary’s Sound, will bring some welcome relief. In this role, it is a valuable anchorage offering shelter in southwesterly winds and being accessible at all states of the tide.

What facilities are available?

There are no facilities at Watermill Cove and all resources are very distant. Hugh Town town is a very pleasant 45 minutes walk.

With thanks to:

Michael Harpur eOceanic