Eric Wright Civil Engineering has completed a £4.8m project to improve the Holden Wood and Ogden reservoirs at Grane Valley, Rossendale for United Utilities.
The 64-week project, which started in July 2012, was commissioned by United Utilities through its ongoing programme of improvements.
The Ogden element of the project saw the Preston-based firm work on the biggest spillway in the UK, a formation which helps water pass over an embankment at a steady rate.
EWCE mechanically lifted 1,300 individual 1.3 tonne wedge blocks into place and poured more than 6,000m3 of concrete.
With the Holden Wood and Ogden embankments being originally constructed in 1841 and between 1905 and 1910 respectively, EWCE had to carry out a number of service diversions in order to maintain the supply of utilities to the surrounding area.
The project also gained attention from the British Dam Society, attracting four times the number of inspectors than usual due to the nature of works.
Adrian Taylor, director of Eric Wright Civil Engineering, said: "We have completed more than 20 large reservoir projects, so our previous expertise proved to be extremely valuable in planning and delivering the work at Grane Valley.
"By working closely with local community groups, such as the Haslingden and Grane Fishing Club, we were able to ensure that our works resulted in minimal disruption, even through some very tough winter weather conditions.
"This work, which saw us pour more than 6,000m³ of concrete, will protect the local area from the threat of flooding and we are delighted to have delivered such a landmark project in our home county of Lancashire."
Jonathan Clarke, project manager at United Utilities, added: "The skill, professionalism and commitment of all those involved in delivering this multi- million pound project successfully was outstanding. Exceptional progress was made against a tight programme whilst maintaining a key focus on health, safety and positive engagement with local residents and stakeholders."