Caretakers Margaret and Martin Smith at Dudding Lake in January 2017, during an algal bloom. Photo / File
Caretakers Margaret and Martin Smith at Dudding Lake in January 2017, during an algal bloom. Photo / File
Dudding Lake has an algal bloom happening and signs are up warning people not to swim - for the seventh year in a row.
The coastal dune lake near Marton is a holiday spot, popular for swimming and boating.
It usually has an algal bloom from the first week inDecember until just before Christmas, operator and Horizons councillor Bruce Gordon said. He runs the facility on behalf of its trust and Rangitīkei District Council.
He expects the bloom to clear in time for the Christmas and New Year holidays.
"The lake is looking really good this year, apart from this small blip at the moment."
In late November algal density at the lake moved to warning level. The organisms are blue-green algae, also known as cyanobacteria.
By December 2 the level had risen further, and Horizons Regional Council water spokesman Barry Gilliland did a second estimate to check. He found an algal density of 13 cubic millimetres per litre - a 10 cubic mm level prompts a health warning.
The species of algae in the lake is not toxic, Gilliland said, but people immersing themselves are at high risk of allergic reactions, such as rashes, itching and hay fever-like symptoms.
The Medical Officer of Health has signs up at the lake, warning visitors against immersing themselves until the algae level reduces. If other years are a good guide, this will happen soon.
Other facilities, including the walkway, at Dudding Lake Motor Camp and Picnic Park, are open.
The Land and Water Aotearoa (LAWA) website rates the lake's life supporting capacity as very poor. It has slowly worsened since 2015.
The regional council monitors Dudding Lake closely. Earlier this year there were fears it was close to "flipping" - being dominated by algae long term. In May scientists considered options for the lake and came up with solutions to improve its health.
Soon after that grass carp, an illegal fish, were found in the lake. The find changed the range of possible solutions.
The one the scientists will now try is the release of more grass carp, to a stocking rate of 32 per hectare. The Conservation Department has given permission for the release.
The carp will eat the lake's luxuriant water plants, giving more space for freshwater mussels (kakahi) to expand their numbers across its sandy and silty bottom. The mussels will purify the water.
