Poplar trees planted decades ago to protect waterways in Northland are now doing the opposite.
Thousands of Aspen poplars were planted along riverbanks from the 1920s to the 1960s to control bank erosion.
But they have now grown so big, they are falling over, taking large chunks of the banks with them and creating dams.
The Northland Regional Council plans to remove two huge poplars that have fallen into the Waihou River, posing a risk to a bridge and power lines.
Councillor Justin Blaikie said the bill would be $10,000.
He said the council has a limited budget for river work that threatens infrastructure, but otherwise the cost falls on landowners.
Mr Blaikie said people with Aspen poplars along streams should consider banding together and felling them before they topple.
He said the timber has some commercial value, if it was offered in large quantities.