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Lake Waikare “culprit” identified

4 June 2014

Lake Waikare “culprit” identified

New analysis has identified the algae causing red blooms in north Waikato’s Lake Waikare this year and it’s believed to probably be non toxic.

The analysis indicates a major increase in a naturally occurring algae known as Monoraphidium in the lake has led to the water becoming noticeably red.

“However, this algae is not one that is known to put toxins into the water,” said Waikato Regional Council water scientist Bill Vant.

“What it does do is send a red colouration into the water around it. If enough of this is produced, the water can be very red.

“Our regular sampling of Lake Waikare indicates densities of the Monoraphidium algae in April were almost 300 times higher than the numbers detected there last year.”

Mr Vant said it was unclear why Monoraphidium numbers were so much higher this year.

“We first started getting reports early this year about red colouring at Lake Waikare and asked then for further analysis to be carried out to try to determine the cause. It hasn’t been till May that scientists at the Cawthron Institute and University of Waikato have been able to confirm the culprit is likely to be the higher densities of Monoraphidium this year.

“Our understanding is that it can be quite common for algae to ‘boom and bust’ from time to time, sometimes for long periods.

“That said, discolouration like this is very concerning and highlights the significant ongoing environmental challenges faced by Lake Waikare and other shallow lakes in our region.”

It is unclear how long the discolouration will continue.

Mr Vant said NIWA’s recent report on the Waikato River catchment for the Ministry for the Environment had highlighted how there was no quick fix to these challenges.

“The council will continue to make sure regular monitoring of water quality at the lakes is done and appropriate information given to the district health board to ensure any appropriate public warning signs are erected.”

The background to the situation at Lake Waikare is that, since the 1940s, multiple human pressures have contributed to the degradation of water quality in this lake and the wider lake catchment. These pressures include such factors as intensive farming and water abstraction to service those farming demands, loss of bank integrity contributing significant sediment, and the re-suspension of sediments by large numbers of invasive koi carp.

A number of studies have been commissioned to look at different actions to reduce these effects. Addressing water quality requires a whole catchment approach with local iwi, landowners and stakeholders coming together to implement a long term plan.

The Healthy Rivers: Plan for Change/Wai Ora: He Rautaki Whakapaipai project – involving the council and river iwi partners - will set targets and limits for water quality in the Waikato and Waipa river catchments. This project, involving all stakeholders with an interest in water in the two rivers, will have implications for lakes such as Waikare and land uses that affect them.

“Water quality in Lake Waikare, and any water body, is highly dependent on the surrounding and upstream land uses. This means that improving water quality requires strong buy-in from a range of stakeholders, in particular local landowners,” said Mr Vant.

Meanwhile, in one project, Waikato Regional Council, assisted by some Waikato River Authority funding, has constructed an automated invasive fish removal and recycling facility at the Pungarehu outlet to help control the abundance of these problematic species.

The Waikato River Authority has also funded other projects aimed at helping the health and well-being of Lake Waikare. These include the enhancement of the eel fishery and riparian planting on the lake edge.

It is likely to take many years, probably generations, before significant improvements to water quality can be demonstrated. This is simply due to the many pressures needing to be addressed and the large size of the lake and its wider catchment.

Council ecologist Dr Bruno David said the situation at Lake Waikare particularly highlighted how rivers and lakes generally were susceptible to the cumulative effects over time of a wide range of land use activities.

“I believe the Resource Management Act could give clearer guidance to regional councils on how to account for these cumulative impacts in their decision-making on water-related resource consents and policies.

“Otherwise there is a risk that consents can be granted for activities deemed to have only a minor impact on water quality, without necessarily taking into account the cumulative effect of a lot of such minor impacts over time.”

ENDS

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