Cleaning up the lake
Recreational users at risk as bacteria levels soar
Waterfowl are stinking up the city’s lake and faecal bacteria is putting recreational users at risk.
Ducks, geese, Australian-banded coots and pigeons make up a large chunk of the avian species dropping faeces into and around Hamilton’s 17,000-year-old Lake Rotoroa. And its future hangs in the balance.
Pigeons have been especially prevalent in recent years, Hamilton City Council’s 2017 Lake Domain Management Plan says.
Bacteria levels in the lake are too high, said water resources engineer and scientist Tim Cox.
Monitoring at sites around the lake, over several years, show elevated levels of bacteria from birds. ‘‘The number one issue with the lake is bacteria,’’ Cox said, ‘‘faecal bacteria that makes you sick.’’
Add to that the nutrients entering the water from stormwater run-off and nutrients already in the lake sediment and you have a recipe for toxic algal blooms with no easy fix. ‘‘We still see the lake go green at times and produce an algae that’s toxic – this blue-green algae that prevents swimability at certain times of the year.’’
There is a willingness to restore Lake Rotoroa to a swimmable standard. But there are also gaps in knowledge and the potential for conflict over what is most important.
The Hamilton City Council is gathering data to find out what the state of the lake is and it is getting help along the way.
The Waikato Regional Council is undertaking a year-long study to test for bacteria in the water, climate research institute Niwa conducts regular tests and Waikato University researchers are testing fish for heavy metals to see if they are absorbing arsenic from the lake bed sediment.
Cox, a member of advocacy group Restore (Restorative Ecological Strategies to Optimise Rotoroa’s Environment), said new data would help devise a way forward. Possible solutions include constructing wetlands, reducing waterfowl numbers, educating people as to what not to put into the stormwater system, expensive engineering solutions like removing sediment or treating with alum.
‘‘In my opinion, there is still some work to do,’’ Cox said. ‘‘Not even just being toxic for swimming but even the look of it – the aesthetic of the lake would improve if we could get those nutrient levels down a little bit and get the algal growth limited.’’
Hamilton City Council parks and recreation manager Maria Barrie said water quality is a key theme in the Lake Domain Management Plan and three steps are in place to achieve it: clarify the state of the lake; identify water quality measures for recreational use; and develop a strategy to improve water quality.
But Waikato University biological scientist Professor Brendan Hicks said the lake has, since 1992, slowly improved in terms of the nitrogen and phosphorus levels, algal blooms and water clarity.
‘‘It’s not going anywhere and as urban lakes go, it’s in pretty good shape, really,’’ Hicks said.
‘‘There is a public perception that it’s a dead lake and nothing could be further from the truth.
‘‘It’s jumping with eight species of fish and it is, in many ways, quite healthy until you go looking and poking around at some of the places with the larger intensities of wild fowl.
‘‘When you do that, you find what you expect to find, which is high levels of poop in the water.’’
The Lake Domain Management Plan looks to manage the birds and fish to ‘‘ensure a sustainable and desirable level of biodiversity’’. It discourages people from feeding bread to birds. Bird seed is suggested instead. But Hicks said it was not as simple as just managing the birds. ‘‘People don’t know what they are managing for,’’ he said.
‘‘They haven’t asked the right questions. If you expect to go canoeing or you expect to go waka ama or swimming, or you just want to fish and maybe eat a fish, then you’ve got to look at the risks and the areas you can do those sorts of things.
‘‘If you are a parent of a 3-yearold, there is nothing more fun than taking your kid down and watching them squeal with delight as the ducks waddle around their feet. Again, that’s another perfectly valid thing you might want to do at the lake.’’
‘‘The number one issue with the lake is bacteria, faecal bacteria that makes you sick.’’
Water resources engineer and scientist Tim Cox