Hutt River clogged with ooze and toxic algae

PAUL EASTON
Last updated 07:14 22/05/2011
river

The Hutt Valley's treasured river.

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The Hutt River is bordered by paths, lined with parks, and peppered with swimming spots. It is the Hutt Valley's playground, but its duties do not end there. It is also the source of most of the drinking water for the Hutt and Wellington.

The river is under pressure. Toxic algae blooms plague it during summer and are believed responsible for the deaths of nine dogs.

Wastewater still flows into the river during wet weather about six times a year when the amount of water exceeds the capacity of the stormwater system.

A proposal to take up to 17 million extra litres a day from the Hutt River may pose a new threat.

Greater Wellington regional council has applied to cut the river's minimum flow for three years during work on water storage lakes at Kaitoke. The work will increase storage by 13 per cent and earthquake-strengthen the lakes.

Hutt city councillors backed the proposal with several caveats, including a halt to the extra take if the river's health suffers.

Councillor Max Shierlaw opposes the plan. "It is likely to reduce the water quality of the river, lead to increased instances of algal bloom because the conditions needed . . . - low flow and warm water - will happen more often."

It highlights a lack of planning for extra water needs by Greater Wellington, he says. "They have no medium-term options and are resorting to trashing a significant regional asset."

CONCERNS about the health of the river led to the formation of the Friends of the Hutt River group this year. "You don't live in the Hutt Valley for the shopping. You live there because of the hills, the beauty of the place, and the river flowing through it," member Pat van Berkel says.

Toxic algal blooms, pollution and low water flows are the group's main worries.

"People are always saying when they were growing up, the Hutt River was full of water."

As the population grows, pressure on the river will increase. "They will all need water, and that's where it all comes from."

Toxic algal blooms stop people using the river at the height of summer. "It's quite a subtle effect, but it's taking away something that is very important," Mr van Berkel says.

Waiwhetu means "star-reflecting water". But poisoned by years of industry waste, the Waiwhetu Stream became the most polluted waterway in the region.

Once home to eels, whitebait and watercress, the stream instead hosted "Waiwhetu ooze", a black sludge, thick with traces of lead, copper, arsenic, zinc and mercury.

A $21 million project to scrape the ooze from the stream's banks wrapped up a year ago, with 56,000 tonnes of contaminated waste removed.

However, Hutt City Council still discharges wastewater, containing untreated sewage, into the stream during storms.

This week, 50,000 litres of treated effluent a day was pumped into the lower Waiwhetu Stream, after a joint in the main sewer pipeline failed at Eastbourne. From there, it flowed into Wellington Harbour. Repairs took four days.

Ted Taylor, Greater Wellington's environmental monitoring and investigations manager, says the Hutt River is "one of the better rivers in the region". Its upper reaches are in "excellent" health, its middle section "excellent to good", and its lower reaches "good to fair".

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That is typical for a river flowing from the hills through farmland and an urban area to the sea, he says.

"You see a decline in clarity, and an increase in algal growth."

Threats to the river include runoff from stormwater drains, likely to increase as the population grows.

People need to realise that whatever goes into the stormwater system ends up in the river, and ultimately, Wellington Harbour, Mr Taylor says.

"If that can happen, we like to think we can maintain the water quality of the river."

Despite the $21m cleanup, the Waiwhetu Stream's quality remains poor. It has low levels of dissolved oxygen, poor clarity, and high levels of ammonia, zinc and nutrients.

Although the cleanup scraped thousands of tonnes of contaminated sludge from its banks, the stream still passes through industrial and suburban stretches, picking up contaminants along the way.

Zinc comes from car-tyre fragments, or washes off galvanised roofs. The presence of ammonia is a tell-tale sign of cross-connections - wastewater systems hooked up to stormwater drains, Mr Taylor says.

"It can be through poor plumbing practices. It may be done deliberately as an easy way out, or it can be a mistake."

Te Atiawa iwi representative Teri Puketapu says the Hutt River and Waiwhetu Stream are of great importance to Maori.

The Hutt River is feeling the strain of a growing population. "When I grew up, all of Naenae was market gardens."

The Waiwhetu was once an important source of food, such as eels and watercress.

"But I don't take anything from it now, and I don't know anyone who does," Mr Puketapu says.

- The Dominion Post

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