New Zealand Transport Agency (NZTA) Central Otago area manager John Jarvis said the willows and poplars were rotten.
About 20 trees would be felled before they damaged the bridge, Mr Jarvis said.
He said if a tree fell on to the metal bridge it could do considerable damage, so it was decided pro-active measures were needed.
"There has been the odd delay to traffic while they fell the big ones, but it's only been a few minutes."
Mr Jarvis said the work was part of an ongoing programme of tree felling on the edges of NZTA's road network throughout the Central Otago and Queenstown Lakes region.
Although not responsible for the work, on Wednesday afternoon the Central Otago District Council got a call from someone upset about the trees' removal.
The caller was referred to NZTA contractor Opus.
