This information asset presents a comprehensive dataset on surface water and sediment quality in the southern section of Lake Macquarie, NSW, Australia. The data was compiled by the Science and Insights Division (S&I) of the NSW Department of Climate Change, Energy, the Environment and Water (DCCEEW) as part of an independent assessment commissioned by the NSW Environment Protection Authority (EPA). The primary objective of this data collection was to support the EPA’s efforts to deliver the NSW Government's response to the recommendations from the NSW Parliamentary Inquiry report regarding the costs associated with the remediation of coal ash repositories. The information serves as a present-day assessment of the contamination status of Lake Macquarie, providing a baseline for evaluating future changes and the efficacy of mitigation and remediation activities. The outcomes of the investigation are detailed in five standalone reports and an accompanying synthesis report.