Abundance estimation is the cornerstone of fisheries management. Mark-recapture techniques based on the Petersen model remains the most often used approach. Few studies compare population estimates against known numbers. The fishing down to eradication of carp in two closed lakes in Tasmania provides absolute population numbers with which to compare the results of several population estimate studies carried out over the past 8 years. A major mark-recapture exercise in Lake Crescent during the summer of 1998-99 resulted in a Petersen estimate of 2053 carp and a Schnabel estimate of 1910 carp remaining. From 2000 to 2002 male carp were tagged and released back into Lake Crescent. A modified Petersen estimator was developed to utilise the mark-recapture information provided by continuing fishing effort during this time. A final conclusive population estimate was instigated in March 2003 with the mass release of 160 tagged adult males. The results of these estimates have proven remarkably accurate considering the large size (23 sq km) of the lake. CPUE based population estimates extrapolated from the Lake Crescent study onto the neighbouring Lake Sorell have precluded the need for releasing any marked fish into this much larger lake.