The Waikato Regional Council is confident that water samples from only 16 sites can estimate levels of E. coli in the rivers of the region

A Waikato Regional Council Environmental Monitoring Officer takes samples from one of the sites monitored for contaminants and toxic algae. Photo / Provided

Although the Waikato Regional Council conducts long-term monthly water monitoring at 125 outdoor recreation sites in the summer to check for levels of E. coli, he says his modeling information shows levels can be confidently inferred by taking samples from just 16 of those sites.

Next summer, the council will test modeling at these 16 reference sites to estimate levels of E. coli in the rest of the region for unsupervised rivers.

He says other regional councils – including Wellington and Auckland – are already using a combination of monitored and modeled results.

Proposals for the development of monitoring programs and an assessment of the 2021-2022 summer recreational monitoring in fresh water, estuaries and offshore beaches were presented at the meeting of the environmental performance committee of the regional council last week.

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Monitoring manager Ed Brown said the changes, including information modeling to include more river sites and greater use of education through web-based platforms and panels, would allow people to decide better. where and when to go swimming.

Brown said the council would also expand the declaration to more lakes where the risk of harmful algal blooms was often high.

“With these lakes, actual sampling may give a false impression that it is okay to swim in them, as monitoring may give the green light for swimming, but, in reality, the situation in these lakes is changing in ways quite spectacular, for example when the wind changes direction, causing seaweed to build up on the opposite shore.

The council will seek to create permanent alerts for high-risk lakes on the Lawa (Land, Air, Water, Aotearoa) “Can I swim here” page using the information available.

The council has had recreational water quality monitoring programs in place during the summer months since 1985.

The programs include 34 monitoring sites at popular sites of open coasts, estuaries, rivers and lakes.

Pepe Bridge in Tairua.  This summer, there were three exceedances above the guideline for E. coli at Pepe Stream.  Photo / HCPost
Pepe Bridge in Tairua. This summer, there were three exceedances above the guideline for E. coli at Pepe Stream. Photo / HCPost

During the 2021/22 season, the concentrations of faecal indicator bacteria and/or the number of cyanobacteria exceeded the guideline values ​​on several occasions.

The open beaches were mostly suitable for swimming, with two cases exceeding guidelines for enterococci – at Buffalo Beach and Port Waikato Beach.

Five estuary sites were monitored over the past summer for enterococci and E. coli bacteria at sites in Kāwhia, Maraetai Bay, Raglan, Tairua and Whangamatā. There were five cases of exceeding the enterococci guideline – four at Tairua Pepe Stream and one at Kāwhia; and four above the E. coli guideline – one in a Raglan motorhome and three at Tairua Pepe Stream.

Nine river sites were monitored weekly for E. coli from December through February (excluding the Waikato River hydro-lakes), with 22 samples found above the recreational guideline. All sampled rivers were affected except for the Waikato River in the Horahora domain, where all results were suitable for swimming.

Water quality in lakes is measured for E. coli (Lake Taupō and shallow lakes) and biological volume of cyanobacteria (Lake Taupō, shallow and hydro lakes). There were three exceedances of the recreational guideline for cyanobacteria in Lake Ohakuri and one in Lake Maraetai.

Elna M. Lemons