Hydro Tasmania manages over 50 lakes and these represent a transformation of the landscape, being referred to as Flooded Lands. Greenhouse gas emissions from these lakes are considered anthropogenic in origin according to IPCC guidelines and should, therefore, be included in Flooded Lands emissions inventories. As Australia’s largest generator of renewable electricity, a proportion of our greenhouse emissions are passed to our customers through their scope 2 emissions. The emissions from Hydro Tasmania’s portfolio of lakes hit our customers’ bottom lines through “net zero” targets that require our customers to offset hard-to-abate emissions. Accepted Tier 1, Tier 2 and Tier 3 methodologies generate significantly different emissions estimates from lakes, ranging over two orders of magnitude, depending on factors such as choice of data period, and decisions made on factors such as how to treat stratification. Measurement based approaches can also produce gross emissions estimates that vary significantly. As businesses and governments set “net zero” emissions reduction targets, accurate” estimations of lake emissions are required in order for them to estimate their offset liability and emission reduction targets. Achieving accurate estimations will require close collaboration between water managers, policy and accounting units within governments, asset owners and the research community.