In 2007, high rates of water extraction combined with a regional drought stopped freshwater discharge to the Coorong, a similar to 120 km estuarine and coastal lagoon system at the outlet of the River Murray (Australia). The sources of organic matter sustaining the Coorong food web in the absence of river-borne organic matter and nutrient inputs were evaluated by measuring delta C-13, delta N-15 and delta S-34 in large-bodied fish and their prey. In general, the delta S-34 of the food web (mean = 11.3 parts per thousand; range = 4.32-18.9 parts per thousand) suggested a comparable contribution from autochthonous pelagic (similar to 21 parts per thousand) and benthic (<5 parts per thousand) primary production. A relatively high delta C-13 in all organisms (-20 to -9.2 parts per thousand) was also consistent with a dominant contribution from autochtonous sources to the food web. A Bayesian mixing model framework (SIMMR) was used to estimate the diet of large-bodied fish for statistically-determined prey groups based on their similarity in isotopic composition. Argyrosomus japonicus preyed primarily on Fish Group 1 (small pelagic fish like galaxiids and Hyperlophus vittatus), Rhombosolea tapirina on Invertebrate Group 2 (polychaetes like Capitella spp.) but Acanthopagrus butcheri fed on a wide variety of fish and invertebrate groups. A partial switch in diet to other prey groups suggested larger Ar. japonicus fed on larger prey, such as crabs and adult Aldrichetta forsteri. Despite being numerically abundant at the time, Fish Group 2 (benthic species) was a relatively low proportion of large-bodied fish diets. This probably reflected the tendency of some salt-tolerant members of this group (such as Atherinosoma microstoma) to prefer hypersaline habitats, which the large-bodied fish avoided. As the heavily preyed-on Fish Group 1 included species with a marine component to their life-cycle, marine productivity may also help to maintain this estuarine ecosystem in the absence of river-borne organic matter inputs. Crown Copyright (C) 2016 Published by Elsevier Ltd. All rights reserved.