Lake Ohinewai is a shallow (4.5 m depth), 16 ha lake in the Waikato region on the North Island of New Zealand that has experienced eutrophication and total loss of submerged aquatic macrophytes since 1983. Invasive fish species such as koi carp (Cyprinus carpio) have been identified as contributing to ecosystem degradation and loss of biodiversity in many North Island lakes. Effective tools for control of invasive fish species has become a priority for governmental agencies. Telemetry tracking of koi carp in the Waikato region has suggested that up to 75% of koi carp undertake migratory movements at some point in their life history. In order to exploit this behaviour, a permanent one-way barrier based on the SARDI push trap was installed on the single outlet to Lake Ohinewai. The barrier was designed to allow passage of adult fish from the lake while preventing their return. When coupled with biomass removals this resulted in a reduction in koi carp biomass from 373 (234 – 513 95% CI) kg/ha in March 2011 to 36.1 (15.3 – 56.9 95% CI) kg/ha in December 2011, 42% of this reduction could be attributed to emigration by adult koi carp. Further surveys in 2013 and 2014 found continued reductions in the koi carp population to 10.4 (3.1 – 17.7 95% CI) kg/ha in December 2014. Analysis of length frequency data showed no significant shifts in koi carp population structure or changes in abundance of other invasive species such as goldfish (Carassius auratus) and brown bullhead catfish (Ameiurus nebulosus) in 2014. Water quality (Secchi disk transparency and total suspended solids) of Lake Ohinewai showed early signs of improvement but submerged macrophytes have not yet recovered. Further surveys will be conducted during the coming 2016-17 summer to determine if changes in population structure or abundance of invasive species has altered since the previous survey in 2014.