IEC2021_SUB_VEG is the spatial representation of submerged vegetation used in the calculation of Index of Estuarine Condition (IEC) scores. In the context of the IEC, 'submerged vegetation' refers to aquatic plants attached to bottom sediments that are generally entirely submerged but may be exposed during very low tides. Field data was collected at various locations within the estuary to ground-truth the mapping of full coverage derived from available aerial imagery. The field data was collected in late spring, summer and early autumn to correspond with warmer water temperatures and longer photoperiods, and to avoid winter periods of submerged vegetation dieback. In the field, ground-truthing by taking photos of the benthic environment largely followed the protocols outlined in Woodland and Cook (2015). If the estuarine bed was visible, photographic samples were collected of the different vegetation types present. Coverages of these different vegetation types (e.g. dense, sparse) were also photographed as well as bare ground. Ground-truthed benthic images were mapped over high-resolution (<20 cm) aerial imagery sourced from the DELWP imagery archive. Only imagery later than 2010 was considered, with most of the imagery used captured later than 2015. RPAS imagery collected for some estuaries was geo-rectified and mosaicked to provide very high-resolution imagery for mapping. Mapped areas were then compared to the geo-referenced ground-truthed benthic images and assigned a vegetation-coverage class and an indication of classification confidence (High, Medium or Low). For each estuary, MA:TV was then derived from the ratio of total macroalgae area to total vegetated area (i.e. seagrass and macroalgae) as per Woodland and Cook (2015). Briefly, vegetated habitat areas were weighted by their coverage classes such that polygons assigned sparse¿medium¿ coverage were considered to contain 50% vegetation, and those assigned asdense¿ coverage were considered as 100% vegetated. The ratio of macroalgae to total vegetation (MA:TV) was calculated as the sum of the weighted macroalgae areas divided by the sum of the weighted seagrass and macroalgae areas. MA:TV ranges from 0 to 1.