The pool was originally a fish pond dating back to 1138 used to rear carp for the monks at Bourne Abbey. It was converted into public swimming baths soon after the Great War of 1914-18 and taken over by Bourne United Charities in 1922 when major improvements were carried out, with the erection of dressing rooms at either end and an approach to the baths from Coggles Causeway. The work of converting it from the old monks' pond was carried out by Mr T Hinson under the direction of a local committee comprising Mr T W Mays (president) and the plans were drawn up by Mr R G Coles, surveyor to Bourne Urban District Council. An official opening by Lady Kesteven was held on Saturday 12th August 1922.

The pool was originally unheated and with corrugated iron sides, and swimmers could often feel the eels wriggling between their toes as they walked on the muddy bottom. 

The picture above was taken from a postcard published in 1936 showing the view looking east towards the railway line with its signal peeping over the fence. The four-tier diving boards had been installed three years earlier in 1933. On the left, we see a busy day at the pool in 1969, a photograph featured in the town guide for that year.

These pictures were taken circa 1946, the one above looking west towards the Abbey Church and below, looking east towards the Bourne to Sleaford railway line with the town's gasometer just visible on the skyline to the left.

The progress of the outdoor swimming pool, as reported by the Stamford Mercury newspaper on Friday 11th August 1933:

 BOURNE'S LIDO: The greatly improved swimming baths at Bourne are proving to be a veritable Lido, and their great popularity is definitely justifying the money spent on improvements by the Bourne United Charity Trustees. It is now ten years since the baths were taken over by the Trustees, the property then belonging to the Vicar of Bourne, as it had done from time immemorial. The site is what was formerly the monk's pond and garden and ten years ago the pond was converted into a swimming bath. There was nothing very elaborate about it - the sides were lined with corrugated iron and the bottom was partly concreted.
But what a great transformation has taken place! Instead, there is now a bath 154 feet long and 50 feet wide, lined with re-informed concrete. The depth of the water at the shallow end is 2 feet 9 inches and at the deep end 7 feet 3 inches. A substantial diving structure has been erected, the apex of which reaches a height of 14 feet. There are in addition two spring boards. A concrete pavement runs right around the edge. The water is supplied by the Bourne Eau and is filtered through a coke bed. It is unique in that the bath is both filled and emptied by the gravity of the water, thus obviating the necessity of a pump. The water flows out through a dyke, passes under the Bourne Eau, and rejoins it further down the stream. A lawn around the sides of the bath has been laid and there are several flower beds and rockeries. 
The only drawback at present is the dressing accommodation, but Bourne readers will be pleased to learn that the present arrangements are only temporary and that next year permanent and more spacious accommodation will be erected.
There are now nearly 300 subscribers, besides casual swimmers. The work of rebuilding the baths was carried out by Messrs Bowman and Sons of Stamford. The baths will close in September for the autumn and winter.

The following week, on Friday 18th August, the newspaper gave more details of the work planned in time for the next year's opening:

BOURNE SWIMMING BATHS IMPROVEMENTS: Patrons of Bourne swimming baths will have the problem of changing accommodation solved for them by the time the baths are opened next season. New dressing boxes are to be erected, numbering over 80 in all. At present, owning to the extreme popularity of the baths, the changing accommodation is being taxed to its limits and during the rush periods patrons have to change behind canvas when the boxes are full. Next season however, this will be altered for the trustees of the Bourne United Charities have approved a plan for the provision of additional accommodation.
The new buildings will be erected in the Abbey Lawn in two blocks facing each other on either side of the convenience. They will be built on concrete and there will be a concrete pathway down the middle. The sides and roofs will be constructed of asbestos. At the monthly meeting of the United Charity Trustees, when the proposed work was approved, the Clerk (Mr H M A Stanton) reported that the total cost of the improvements to the swimming baths was £1,242 10s. 3d. [almost £70,000 by today's values] which was £46 10s. in excess of the estimates. The excess was entirely due to the cost of the new diving erection and lavatories, which were not included in the original estimates. It has been decided to curtail the attendance of children during the evenings when mixed bathing is allowed.