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It is thought St Helen's Loch was man made to create water for the industry that once flourished in High Bonnybridge, on the south bank of the canal. Indeed, at the "Radical Pend" there is a plaque stating that the water flowing out of a tunnel and through the Pend has originated at the loch.
The oldest map I can find (see images below) is from the 1840s which clearly show the loch with a dam and sluice at the west end, then a stream runs down to a smaller loch and sluich at the now long gone Broomhill Distillery, and then continues down to the Tile Works. The other loch is gone too but the remains of the sluice can be found right next to Antonine Primary School where the stream still flows under the road. Moving forward to 1888 to 1915 you can see the addition of filtering beds after the sluich at St Helens Loch and that it provided water to pretty much all the industry to the south of the canal. Nowadays much of the stream is hidden below modern High Bonnybridge but still makes an appearance on its journey through the town.
On the north shore of the loch is an small hill. I assumed this was man made when the loch was dug out. From a bit of research and an article from Greenhill Historical Society this is Elf Hill, a mound of moraine which was laid down by a glacier during the ice age.
The loch itself is a haven of bird life and its nice to spend a bit of time here watching the wildlife.
From the Loch it is a short walk through the field to Rough Castle, a Roman Fort which was built on the Antonine Wall. There is sometimes cattle in this field, although it is a right of way, so keep Geomutts under control.
Maps courtesy of the National Library of Scotland
