Lake's quality on agenda

A group of professionals are lobbying to improve the quality of Hamilton lake, with hopes to see it swimmable by 2020.

The group 'Restore' is made up of 10 professionals from various areas with the aim of improving the water quality of the Lake Rotoroa, also known as Hamilton lake.

The group plan to make submissions to council as part of the Hamilton Lake Domain - Reserve Management Plan. Hamilton Lake has had issues with algae, making the lake unsafe during warmer periods of the year.

David Menkes, MD PhD, medical academic and pharmacologist, and founder of the group with partner Jill Masters, said the process of bring the lake back to a standard which people desire would need to be broken down into steps. There are three main areas to address: heavy metals, fecal coliforms (from ducks and other wildlife), and nutrient overload.

"Each of those three areas has a different source and a different set of strategies which would address it to some extent," Mr Menkes said.

While still in early stages, suggestions from the group include aeration and dredging, feeding ducks on land or in another area rather than in the lake, removing plant matter, and sediment remediation such as treating the water with the chemical alum, which is used to purify water, or crab-shell extract.

Aeration can be achieved through the infusion of air into the bottom of the lake, lagoon or pond or by surface agitation to allow for oxygen exchange at the surface and the release of noxious gasses such as carbon dioxide, methane or hydrogen sulfide.

Kevin O'Shannessey, environmental advisor, Waikato Raupatu River Trust, said initially it was thought the issues could be resolved primarily by only using aerators but since realised the arsenic content from sprays used in the 1980s meant several issues would need to be addressed.

"When we realised there was arsenic in the bottom we realised it was more than just aerators that are needed. A blunt way [to get rid of it] would be to dredge the lake."

Mr Menkes said various options could be considered including removing plant material, which takes up the heavy metals and overload of nutrients causing the issues in the lake.

"One of the characteristics of this lake is it functions as a stormwater catchment. One theory would be to treat or process the stormwater as it comes in, so rather than have big pipes coming in from a roadway, vent it into some stream or creek where you have plants and soil, which could filter it. That would do a good job of [getting rid] of those nutrients like phosphorus and nitrate."

Mr O'Shannessey said there needs to be a long-term comprehensive plan for the lake.

"From our point of view, as long as there is a process and it is moving through and if it does take one or two generations everyone is still on the same page.

"The concern that we have is that councils, nothing has been achieved out of (the current plan). They're about to review it but of course we have a whole lot of new faces and new ideas instead of having a cohesive plan that carries over 20 years and every five years you go ok, 'what did we do in that five years, the next five year step is this'.

"What you get is each time they change their mind on how this should look, it is very easy for a group of councillors to say well you have no direction therefore you do not need the funding. The chances are if it is going in [the right] direction we could find the sponsorship for the shortfall."

Council's Parks and Open Spaces Unit has been monitoring and managing the algae issue for about five years, along with several other councils in the Waikato. Council will this year look to collaborate with experts to determine a solution to this problem.

In an effort to mitigate some of the algae-related issues, council has undertaken some work around the periphery of the lake, focussing on improvements to the quality of stormwater into the lake.

Their aim is to reduce the amount of nutrients and sediment going into the lake during stormwater events.

Addressing the algae issue is on council's agenda over the next 12 months.

Group members

David Menkes, MD PhD, medical academic and pharmacologist

Kevin O'Shannessey, environmental advisor, Waikato Raupatu River Trust

Tim Cox, PhD, water resources and water quality modeller

Michael Kahan, MB ChB FACOEM, occupational and environmental physician

Robin Janson, PhD, microbial ecologist/agricultural microbiologist

Anna Cox, PhD, project coordinator, Waikato Environment Centre

Rob Ebert, MB ChB, secretary, Hamilton Yacht Club

Alexander Gillespie, LLB LLM PhD, Professor of Law, University of Waikato

David Hamilton, PhD, Professor in Lake Restoration, University of Waikato