In August, a complaint was made about a 1080 drop at Otira after several poisoned baits were discovered outside the operational area.
The EPA said there was no evidence from the flight lines showing the permitted boundary had been breached.
"It is uncertain how the baits came to be outside the operational area. However, it may be a combination of the very steep landscape in the gorge with baits falling on to rocks and bouncing downhill, and that GPS is not 100 per cent accurate in such steep terrain. It's also possible that wind was generated by the gorge terrain."
The report found the 1080 regime was working as intended with the benefits of using 1080 being seen while the risks were minimised.
The EPA received 57 reports of aerial 1080 operations, covering 448,210ha almost a quarter of that on the West Coast.
There were eight breaches of the Hazardous Substances and New Organisms (HSNO) legislation controls, which occurred during seven operations. That is up from five reported in 2012, but is below the 11 reported in 2011. The EPA noted there had been an increase in 1080 use, so it was not unexpected.
Post-operational water monitoring was carried out for 17 of the aerial 1080 operations last year, with over 70 individual tests reported. The tests can detect down to 0.1mg of 1080 per litre of water. No samples contained concentrations of 1080 above the method detection limit.
EPA chairwoman Kerry Prendergast said the majority of incidents were reported by operators and funding agencies rather than by members of the public or other agencies.
"Operators are following our communications guidelines, and making sure to engage with locals and iwi," Ms Prendergast said.
