Believed to be Scotland’s oldest reservoir, Gartmorn Dam by Sauchie is the largest expanse of water in Clackmannanshire at around 170 acres and, for a time, served as Alloa’s water supply.

The dam was formed on marshy ground and was the brainchild of engineers working for John Erskine, 6th Earl of Mar, who, in 1700, made a dam-head at Forestmill and flooded the hollow at Gartmorn until it reached a depth of 11.2m (37 feet), leaving a little island in the middle.

The initial temporary dyke was replaced in 1785 by one of hewn stone, but damage to it meant that in less than 50 years the whole structure had to be repaired by John Craich, the manager of Mar's Alloa Colliery Company at a cost of £300.

One of the dam’s purposes was to collect water all in one place rather than gathering elsewhere causing damage to crops, livestock, homes or businesses.

Its main purpose, however, was to drive pumping machinery to drain water from the Earl's coal mines.

In 1710, he commissioned Derbyshire based engineer George Sorocold to write a report on how to deal with water ingress at his Sauchie mines as coal was being extracted at ever deeper levels.

The reservoir at this time was fed by the Brothie Burn but he proposed increasing its capacity by diverting water from the River Black Devon.

He suggested a feeder stream to take water from the river at Forestmill. This in turn would also potentially increase power output.

Sorocold told Erskine that two water wheels should be used to power the pumps for extracting the mine water, but the Earl ignored this advice and water was still extracted using rag pumps and chains and buckets many years later.

By the time he had finished his work, Gartmorn had risen by 3m (just over 9.5ft), making the body of water now 1.2km (0.7 miles) long by 500m (546 yards) wide.

A 1.82m (6ft) high horseshoe-shaped weir was built at Forestmill and a two-mile-long lade was constructed to feed Gartmorn Dam, and the increase in water was used to drive pumps to remove water from the mines which was diverted to an area near the dam via the Upper Lade.

The Lower Lade was used to power the industries in Alloa and in 1891 the Burgh of Alloa acquired the system.

Thanks to Gartmorn, Alloa boomed and became known as the ‘town built on water.’

The weir at Forestmill was rebuilt in 1835 and in 1972 was Category B listed.