Landcare Research water testing of the Brook Stream (pictured) post poison drop shows "no detectable residue" the Brook Sanctuary says.

No detectable residue has been found in the Brook Stream following a poison drop at the Brook Sanctuary, the trust says.

The Brook Sanctuary dropped the first 11.5 tonnes of bait laced with brodifacoum on September 2, with two more drops to follow before the end of October.

Brook Waimarama Sanctuary Trustee Derek Shaw said the testing showed the water in the Brook Stream "as it flows out of the Brook Waimarama Sanctuary and further downstream" had "no detectable brodifacoum residue".

One of the helicopters involved in the poison drop at the Brook Waimarama Sanctuary.

Shaw said eight samples were collected by Cawthron Institute from the Brook Dam and the Brook Stream at Hockey Place before the aerial drop, and 14 hours, 23 hours and 47 hours after the operation.

The analysis of the samples was done by a Landcare toxicology laboratory.

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MARION VAN DIJK The Brook Waimarama Sanctuary says water testing shows no poison residue has been detected in water tests following the recent poison drop.

Shaw said the results indicated "testing of all samples was below the method detection level of 0.02 parts per billion of brodifacoum in the water".

"We knew it was highly unlikely the Brook Stream would be contaminated as brodifacoum is insoluble in water," he said.

Brodifacoum is a common rodent poison that is toxic to humans and animals. The Brook Sanctuary operation aims to eradicate all predators from within a 14km pest-proof fence that was completed last year at the 691-hectare sanctuary, to allow for the reintroduction of native wildlife.

About 26.5 tonnes of poison laced pellets will be dropped in the three drops, with about 500g of brodifacoum used in total. The drops are spaced approximately three weeks apart depending on weather and other factors such as availability of helicopter pilots and transport operators.

The Brook Valley Community Group protested against the use of brodifacoum in the Brook Sanctuary on Saturday at the Nelson Market, followed by a standing protest at Anzac Park. The protest was part of the National Ban1080 March.