© Anna-Marie BakosThe disease is mostly affecting waterfowl including ducks and gulls.
The Department of Conservation and Fish and Game are working with the Pukorokoro Miranda Shorebird Centre to contain the outbreak.
The wetland is home to tens of thousands of rare native and non-native waterfowl and shore birds and it's estimated around 200 have died so far.
Fish and Game said it's an unfortunate thing to happen, especially in a significant wetland like Miranda.
"There is a botulism outbreak, which is a very serious bird disease. It is caused and spread by poor oxygen levels in the water - the birds ingest it and it's all over." said Don Rood, Fish and Game spokesman.
"It's not a nice way to go, it paralyses them then they die."
Rood said there's little that can be done, aside from burying the bodies, so the bacteria can't spread and re-enter the environment to infect healthy birds.
"What we're worried about is the deterioration of the general environment, when things like this happen there is a tendancy to down play it but anything that is killing birds in such a way is a concern." Rood said.
Department of Conservation Wildlife Vet Kate McInnes said this is a case of avian botulism and poses no risk to humans.
"It's triggered by environmental conditions which prompt a bacteria, found naturally in soil, to produce a toxin that cause birds to die."
McInnes said that botulism outbreaks usually clear naturally when rain and cooler temperatures change the conditions that triggered the outbreak.
The Miranda Shorebird Centre manager Keith Woodley said the outbreak of disease is concerning and has been killing waterfowl and shore birds over last two weeks.
"There is always concern when it's affecting our wildlife, but it's important to remember that outbreaks of this nature are not uncommon in this country, especially when conditions are warm and dry.
He added that the disease has so far only affected a small portion of the tens of thousands of birds in the wetland area.
Dead birds found at Pukorokoro Miranda have been sent to Massey University for testing to try and establish the cause of death.
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