In response he had "copped a fair bit of abuse" from the boys, who he guessed were aged between 12 and 14. He did not get a photo because he suspected his phone would have ended up in the stream.
Rod Brown, the main driver of the Wairoa Stream walkway project, reported the incident to the police in Kerikeri on Friday morning.
The walking track had been built with thousands of hours of volunteer labour and was funded by public donations, so it was frustrating when time and money had to go into repairs, he said.
Volunteers from the Friends of Wairoa Stream had spent four hours on Monday securing the first boardwalk with reinforcing steel and 50kg of concrete. They had also replaced a stolen safety rope along a steep section of track with wire, which would be less attractive to thieves.
Four signs had also been stolen in recent months, though that was probably unrelated, and one sign asking people not to take dogs through a stretch of private property had been vandalised.
Mr Brown said volunteers had been diverted from essential weed control to carry out the repairs. It was likely they would have to secure the second boardwalk with concrete as well.
Vision Kerikeri's latest project was installing rat traps along the trail.
"It's just a pity there are no traps for idiots," he said.
Anyone who knows who is responsible for the vandalism is asked to call in at the Kerikeri police station or phone the non-emergency line on 105.