The aim of the research presented in this paper was to conduct a study on the extent of the fatigue impact on the productivity of a construction crew in a dam construction project in Queensland, Australia. It was also aimed to examine economic implications associated with the affected productivity due to fatigue and to provide recommendations for improvement. To achieve the research aims, the Palm Psychomotor Vigilance Task (PVT) reaction tests were used to measure the reaction time of a sample of concrete crew members at different times during the day onsite over a one-week period. By measuring the reaction times of workers, the relevant levels of fatigue were determined. Productivity was measured using the Labour Utilisation Factor (LUF) by observing productive, supportive and non-productive times of the sampled crew onsite. The results from the tests showed that fatigue was present in sampled workers. The highest levels of fatigue were found to be due to high temperatures and physical exhaustion. The results showed that as fatigue increased among workers, the productivity dropped. It was found through a correlation analysis that fatigue had a negative association with the level of productivity. It was also found through productivity analysis that the average cost due to fatigue causing decreased production rates was $50,000 per annum for a concrete crew consisting of 10 members. The main recommendations were to mix the work between difficult and simple work for crew members, scheduling to arrange this mix, and allowing short breaks while temperatures and humidity is high. Some other suggestions include the use of salt tablets to minimise fatigue caused by dehydration and an increase of shaded areas for worker breaks on the spillway.