Recent heavy rain across the Wellington region has killed off large amounts of unwanted species in the harbour.

Scientists have been on the hunt for overseas marine animals and plants that are classed as non-indigenous marine species (NIS) that can have detrimental impacts on New Zealand's environment and economy.

Although the wet weather may not have been the summer sunshine locals had hoped for, it was a positive for NIWA's bi-annual biosecurity survey.

Results showed the rain had caused significant mortalities in some shallow-water locations to already established populations, and prevented any new signs of NIS, too.

Marine ecologist Chris Woods said the results from the survey was "good news for our native species".

"It seemed to kill off NIS at locations where these invasive organisms can predominate over native organisms."

The survey covers 12 major ports and marinas, including Wellington, Ōpua Marina/Waikare Inlet (Te Moana o Pikopiko-i-Whiti) in the Bay of Islands, and Bluff Harbour (Awarua) in Southland.