Red Weed Lake

Pond Weed Blight Harmless

Says Kapiti Coast Council

January 26, 2010

There is a mat of red weed covering much of the northern end of the Waimanu Lagoon at Waikanae Beach, but it is not poisonous, says the Kāpiti Coast District Council.

The KCDC’s Leisure & Open Space Manager, Lex Bartlett, says:

“It’s a native plant called Red Azolla, (Azolla filiculoides).

“It spreads very quickly in the right growing conditions and is found in ponds and lagoons that don’t have much in or out flow,” he says.

“It’s naturally occurring in such ponds in our area, but normally is not found in this lagoon.

He says “It is well established in the Waimeha Lagoon, which I suspect is where it has come from — either via wild life or through the connecting waterway.

Weed ‘not poisonous’

“It is not poisonous and does not affect the wild life. In fact with its shading of the water it may well improve water quality and reduce the growth of other water plants as the water does not heat up as much in the summer.” says Mr Bartlett.

“The plant normally reduces significantly in cooler months,” he says.

“It’s our view that the plant should be left alone as it is naturally occurring as part of the local ecology and does not affect water quality or the wildlife.”

Mr Bartlett says: “However, we understand that some people may argue that it is a little unsightly.”

Three Options Open to Council

He says there are three options open to the Council to remove the weed, but none of them are likely to be particularly effective or long lasting.

He adds: “Firstly we could lower the lagoon levels again as we did just before Christmas, however to have any real effect it would need to be low for a considerable period.

“And it is not likely to be very effective as any weed left multiplies very quickly and it would soon it be back to current levels if suitable growing conditions continue.”

“The second option is to use chemical means, but that is not acceptable in this environment,” he says.

“And, finally, the weed could be removed manually.  This option too is not very practical due to the cost, the human resources required and the fact that once again it would be only a short term fix as any plant material left will soon multiply back to current levels.”

He concludes:  “It may not be pretty but it is harmless and it will go away in the winter months,” he said.