There is a close relationship between climate system and quality and quantity of freshwater resources. Due to this relation, climate change becomes an important factor affecting quality and quantity of freshwater resources for human use. Moreover, climate change is generally projected to have adverse impacts on water quality of freshwater ecosystems particularly in zones with Mediterranean climates. Many studies have evaluated impacts of climate change on water quality of elements of freshwater ecosystems such as natural lakes and streams. However, limited information is available on man-made ecosystems such as reservoirs that are mostly under influence of natural environmental conditions. This study emphasizes importance of understanding impacts of climate change and extreme weather events on water supply reservoirs to improve management practices for water provision. A deep reservoir (Lake Bellfield; max depth 36m) and a shallow reservoir (Lake Wartook; 8m) in eastern Grampians Ranges, near Halls Gap in Western Victoria, Australia have been chosen to understand historical water quality transitions. They represent good case studies as they have both experienced recent floods and fires which caused water quality issues that impacted water supply for Wimmera Mallee community. Moreover, while there are concerns about water quality, particularly after floods and fires, only irregular detailed monitoring has occurred to date. Thus, there is currently little or no coherent understanding of historical water quality transitions of these lakes. This study will measure a range of water quality parameters as well as hydrodynamic characteristics of both lakes. Monitoring to date has focused on water quality parameters which have the most potential to impact on water supply operations. Additional monitoring and paleolimnological assessments will be undertaken to better understand mixing characteristics of the lake, to help inform future operations of reservoirs following influx of sediments and inflows after extreme weather events like floods or fires.