A dreaded worm, known as "termite of the sea", has been blamed for the collapse of the Nuhaka rail bridge last month.
After examining the two wooden bridge piers that failed, sending a 60-tonne rail crane tumbling into the Nuhaka River, investigators for the government's rail infrastructure company Ontrack have
found the timber below the salt water line had been weakened by attack from the teredo worm.
The worm had not previously been detected in the river, in the Wairoa district, and Ontrack normally only checked for it on bridges on the rail network much further north, said Ontrack boss William Peet.
Mr Peet said a National Institute of Water and Atmospheric Research scientist was investigating if climate change could be to blame for the worm's presence, and helping to identify the marine organisms in estuaries.
"There was no history of the worm's presence in this estuary and few signs in the inter-tidal area that a suitable micro climate for the organism existed," he said.
Mr Peet said the investigation would establish the exact cause of the bridge's collapse.
Commonly known as the ship or pile worm, the teredo is a bivalve mollusc which invades wood as a tiny larvae and grows quickly to between 15.24cm and 1.82m in length.
The teredo has been described as a nightmare for waterfront property owners as it turns wood into a brittle honeycomb.
As a precautionary measure all 48 other timber bridges crossing estuaries on the rail network had been checked by divers.
They found three bridges had been attacked by the "termite of the sea" and these had been repaired, Mr Peet said.
The 120m long steel and timber bridge on the Napier-Gisborne railway should be repaired by the end of this month, Ontrack said.
- HAWKE'S BAY TODAY
