Toxic algae clears

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Good news for all those who prefer a dip in the river to the ocean this summer.

The latest monitoring of Tasman’s rivers shows either no or very low concentrations of toxic algae at most sites.

Tasman District Council environmental information manager Rob Smith says the Wai-iti River at Brightwater Bridge is the only site that still has notable concentrations of the potentially toxic cyanobacteria algae, with 12 per cent coverage recorded on 12 January 2016.

While this is below the level at which warning signs should be erected (20 per cent is the Ministry for the Environment’s guideline), the growths are very patchy at this site so Rob encourages people to continue to take care with dogs and small children around the water.

“We’ve left the signs up at this site as we expect that the coverage will approach 20 per cent very quickly again.”

The algae are known to be deadly to dogs and pose a potential health risk to humans, with the toxins capable of causing vomiting, diarrhoea, abdominal pain, cramps, and nausea when ingested. It is wise to not enter the water where the algae are visibly building up.

“Because the recent rain gave the rivers a bit of a clean-out, most of our popular swimming spots are looking pretty clear of the algae at the moment, which is great,” Mr Smith said. “The algae can spread very quickly in the right conditions though – when we get stable flows and hot and dry weather – so it pays for people to continue to keep an eye out for visible patches of it. It’s relatively distinctive because it forms soft, dark-coloured mats with a jelly-like consistency.

“We’re doing weekly monitoring of popular swimming spots, including the Lee, Roding, Takaka, Waimea and Wai-iti rivers, and the latest results will be posted regularly on our website if people want to see what the levels are before they head out for a swim.

“With low toxic algal cover and good water quality, everyone can get out and explore our world-class rivers and beaches.”