RSPB's Llandudno Junction reserve salt water to kill swamp stonecrop weed
Salt water is to be used to kill off a weed which threatens a freshwater lagoon at an RSPB reserve where thousands of birds feed on mud flats.
About 7m gallons (32m litres) is being pumped from the River Conwy into the lagoon at Llandudno Junction from high tide on Thursday.
It is designed to eradicate an invading weed from Australia, known as swamp stonecrop, or crassula helmsii.
The lagoon had already been emptied and will be kept salty for at least a year.
It is thought to be only the second time that salt water has been used to tackle the plant in the UK. It was used successfully at the RSPB's Old Hall Marches reserve in Essex.
The project is being jointly funded by RSPB Cymru, Environment Agency Wales and the Countryside Council for Wales (CCW).
"If we don't undertake this work, crassula could smother the mud and reduce its value for birds, and the lagoons could be a source to spread the weed to other places in the Conwy Valley," said Dave Thorpe, Environment Agency Wales' biodiversity technical specialist.
RSPB Conwy includes part of the estuary, providing a convenient source of saltwater.
Warden Sarah Money said salt was the one thing known to kill the plant.
"This provides a great opportunity to assess how we could undertake similar measures within the much larger adjacent lagoon," she said.
Additional freshwater habitats were created last year for amphibians and dragonflies, which cannot live in saltwater, but she said most water birds would not mind.
"Initially the reeds may be weakened, but it's an impressively tough plant that is quite capable of surviving the temporary brackish conditions," she added.
Dr Neil Smith, from CCW, said it was not known how the weed arrived at the reserve, but it is widely imported on aquatic plants bought for garden ponds.
"It is sold as an oxygenating weed, but is thought to be causing millions of pounds worth of damage to wildlife sites across Wales, and elsewhere in north west Europe," he said.
The work will mean part of the reserve trail will be closed, but the rest of the reserve and its facilities will be open as usual.