Plant matter covering a lot of Tower Lakes, Paraparaumu, is a native plant called azolla, not algae, council biosecurity programme manager Rob Cross said.

"This plant doesn't pose a serious environmental threat and doesn't have adverse effects on wildlife.

"Accumulation like this on top of a pond is natural for a small closed body of water and tends to be seasonal, so it's likely to die back in winter.

"It's usually eaten by waterfowl but when it grows quickly they can't keep up, which is why it's more noticeable at the moment.

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"It can be removed manually using a rake or moveable boom as it sits just on top of the water."

There are around 100 ponds in the district including both privately-owned and council-owned ponds.

The pond on the corner of Langdale Ave and Kapiti Rd is privately-owned, which means it's not maintained by the council, and it is up to the private owner to carry out any works related to their ponds.

However, last month the council started a new inspection programme on all ponds in the district and will eventually report back on the status of each pond. If council find there are cleaning or maintenance needs for a privately-owned pond, they will get in touch with the owner to talk about steps they could take to improve the condition of their pond.