Lakes’ health lackluster
Lakes in the wider Manawatu¯ region are in dire health, as all those being constantly monitored score extremely poorly under national standards.
And, elected officials have been told the clean-up bill will be costly.
Horizons Regional Council natural resources manager Jon Roygard gave that blunt assessment at the council’s strategy and policy committee yesterday.
Although there are 200 lakes in the region covered by the council – from Horowhenua to Ruapehu, and Whanganui to Tararua – Horizons only monitors 15 for reporting purposes.
That is a big improvement from 2014, when only one, Lake Horowhenua, was monitored.
Roygard said there were big gaps in the monitoring network – no Manawatu¯ lakes were checked despite the district having more lakes than any other district within Horizons’ boundaries.
The monitored lakes almost all came in at the unhealthy end of the spectrum.
One way of ranking lakes, the Trophic Level Index, scores their health from one, which is good, to 10. Most lakes in Horizons came in at six or seven, Roygard said.
More detailed information showed all monitored coastal lakes failed to hit nitrogen targets under the One Plan – Horizons’ environmental regulation framework.
Almost all failed targets for phosphorus and chlorophyll-a – the pigment that makes plants and algae green.
Lake Horowhenua coming back as having passable levels of ammonia had to be taken with caution and Roygard said levels were known to get high enough to kill fish.
‘‘The results show we have a lot of work to do.’’
Lake Koitata, on the west coast of Rangitı¯kei, was the only one to score any A-grades under a system in the National Policy Statement for Freshwater. But it still fell short in some areas.
Some lakes were at risk of becoming algae-dominated, with Dudding Lake in Rangitı¯kei near the top of that list.
Other lakes had high ph and low oxygen levels in different parts of their waters, which could lead to nutrients being pulled from both the top and bottom of lakes, he said.
Work was happening at some lakes, most notably ones used for recreation, but it came with a cost.
About $7 million had been sunk into Lake Horowhenua in the past decade and there was more work to come, he said.
Government money was available for cleaning up lakes, but there needed to be good information about them and what was required first, Roygard said.
Councillor Rachel Keedwell said she wanted lake health to be looked at on a wider scale, preventing problems upstream rather than dealing with them at lakes.
She called for action. ‘‘The scale of the problem is huge. We can monitor and see what a crap state most of them are in, but I would like to see a lot more attention given to what can be done.’’
Cr Bruce Rollinson agreed monitoring was good, but getting something done was better.
He wondered if it was possible to buy land around lakes and do riparian planting and fencing to protect them.