Stakeholders' Participation in Monitoring and Evaluation (M&E) is a critical factor in determining the performance and success of projects across various sectors. Effective stakeholder engagement ensures that the voices and perspectives of all relevant parties, such as government agencies, local communities, NGOs, and consumers, are heard and considered throughout the project lifecycle. By actively involving stakeholders in the M&E process, projects benefit from their valuable insights, leading to better-informed decision-making, improved project design, and enhanced transparency. Ultimately, this collaborative approach contributes to more efficient and sustainable project outcomes, addressing the diverse needs and interests of the stakeholders involved. The study adopted the descriptive research design. The target population was 250 stakeholders in Water Supply Project (Cotter Dam) in Australia. The study did sampling of 220 respondents that were chosen from the target population of 250 stakeholders of Cotter Dam in Australia. Questionnaires were used to gather the data. In conclusion, the evidence from the Cotter Dam project in Australia underscores the critical importance of stakeholder participation in Monitoring and Evaluation (M&E) for the successful execution of water supply projects. Active involvement of stakeholders, including government bodies, environmental organizations, local communities, and consumers, leads to improved decision-making, transparency, and accountability throughout a project's lifecycle. By embracing lessons from the Cotter Dam, future water supply projects can adopt more inclusive, transparent, and collaborative approaches, ultimately ensuring the continued success and sustainability of critical infrastructure initiatives. The study recommended that to enhance the effectiveness of stakeholder participation in Monitoring and Evaluation (M&E) for water supply projects in Australia, it is crucial to establish robust communication channels that engage a diverse range of stakeholders, from government agencies to local communities. Additionally, clear policies and guidelines should be implemented to ensure mandatory stakeholder involvement and accountability, fostering a more inclusive, transparent, and successful project execution.