Green invader gets into lake bay

Department of Conservation staff at Lake Waikaremoana believe a boat owner may have inadvertently introduced a noxious weed to one of the bays on the lake.

During a dive survey being carried out as part of an annual inspection of the waters, a small infestation of lagarosiphon (oxygen weed) was found growing within Te Raoa Bay off Whareama Peninsular.

The bay had since been closed off.

Te Urewera Whirinaki Area's acting southern biodiversity manager Mark Lewis described the discovery as "disappointing" and said as the survey continued it was possible more patches of thick, mat-like weeds would be found.

DoC staff have begun eradicating the plants, which cover about 200sq m, and are advising all boat users at the lake to be aware of the find and to keep away from the affected area.

Mr Lewis said it is unknown how the plants got into the bay "but it is most likely that a small piece was transported from another waterway on a boat".

He said a piece as small as a $1 coin was enough to get another plant started so boaties needed to be vigilant when moving their craft or swimming gear from one waterway to another.

"Preventing spread is a whole lot easier than cleaning up the problem," Mr Lewis said.

The plant is epidemic in the lakes at Tuai and Kaitawa, where it thrives in the shallow water and sheltered conditions to form thick mats.

The last discovery of the weed at Lake Waikaremoana was at Rosie Bay in 2010 and it was successfully removed.

FACT FILE

Lagarosiphon was sold as an ornamental pond plant and is believed to have entered the country's waterways after being disposed of in drains.

It grows rapidly and can smother and eventually take over native vegetation.

It also reduces the availability of oxygen to fish life, affects whitebait availability and impedes fish access to spawning areas.

It increases sediment and for the angler it becomes a menace as it tangles and snags lines.

 

Email: roger.moroney@hbtoday.co.nz