Biosecurity New Zealand is overseeing post-mortems and toxicology tests after the dead birds, which included 85 paradise ducks, were found at Dublin Bay on Monday.
The agency's main role was to determine if exotic (introduced) disease was involved in the deaths, a spokesman said.
'Large numbers of dying birds are not uncommon and can have environmental causes such as algal blooms and botulism.
"Samples will be analysed by our Animal Health Laboratory and we expect the results later next week."
Fish & Game staff found 85 dead paradise shelducks and a mallard duck on the lake margin and in a nearby paddock yesterday morning, Fish & Game officer Bruce Quirey said.
Members of the public also removed a dead black swan, nine Canada geese, three paradise shelduck and a mallard on Monday.
Fish & Game staff inspecting the site saw no signs of physical injury causing the birds’ deaths.
Members of the public were advised not to touch any more of the dead birds, but to keep pets away and advise authorities.
