The restoration of Northland's Lake Omapere has reached a "significant milestone" with the introduction of almost 20,000 adult grass carp and reduced weed growth over summer.
Northland Regional Council environmental manager Tony Phipps said the release of carp into the lake, 26km northwest of Kawakawa, had gone ahead as planned.
The council
abandoned plans to spray herbicide to control weed in the lake because the weed did not grow as much as expected over summer.
The slow growth was probably due to moderate summer conditions and an algal bloom that shaded the weed.
Mr Phipps said that although there was still work to be done, the reduced summer weed growth and introduction of the carp had been a "significant milestone".
"We are optimistic about the outcome of these weed control actions," Mr Phipps said.
It was expected that the 20,000 fish, as well as those introduced by the Lake Omapere Trustees and New Zealand Water Management in 2000, would be adequate to control the lake's weeds.
The fish intake was likely to break the boom and bust cycles of algal blooms and weed collapse in the lake.
Over time, experts hope to see Lake Omapere re-vegetated with native turf plants to stabilise the bottom sediment.
An increase in freshwater mussels was also expected, Mr Phipps said.
Mussels had effectively been the lake's filters, removing algae and helping to keep the water clear.
Up to 90 per cent of the mussels in Lake Omapere died about a year ago after oxygen levels in the weed-infested lake dropped.
- NZPA
nzherald.co.nz/environment
