Westport beaches are being monitored after more than 600 dead rats washed onto shore.
Carcasses have been sent for testing as the Department of Conservation works to find out why it happened.
Spokesperson Mark Davies is perplexed, saying it is not normal.
"We have put - with support of the Buller District Council - signage up on the beach, for people who are taking their dogs. Nobody wants their dog eating a half-decomposed rat."
Davies says it is not inconceivable the rats could have washed out of the hills by heavy rain after a 1080 poison operation 140km away.
Autopsies are being done.
- Aerial 1080 could combat 'tsunami of rats' far better than trapping
- Rats wiped out, 80 percent of possums killed, after 1080 drop in Northland’s Russell Forest - DOC
Davies says the discovery was made by a member of the public who stumbled upon some rats at high tide.
"They'd obviously been in the water a couple of days and they were starting to decompose. It's not a pleasant sight and needed cleaning up. We need to find out what's caused it."
Davies doesn't think 1080, a controversial poison used in pest control, is the cause, because reports of dead fish and birds - along with the rats - are not consistent with the way 1080 is understood to work.
"We're sending off dead carcasses to get autopsies and toxicology (tests) on them, so we'll find out what actually causes this - but it will take a few days."
Locals are being warned to keep their dogs off the beaches.
Newshub.
