Mr Golder, who captured video footage on his phone, said he did not know who the people were.
The surfer was not going "very fast or hooning along like some kind of demon" and he was not impacting on anyone else's safety, he said.
"It was merely two people who decided to have bit of fun on a wet day, and if there was any risk to anyone, it was to themselves."
Tauranga City Council communications advisor Marcel Currin said motorbikes were not allowed on reserves.
"Also, stormwater reserves are not healthy places to swim in, especially after heavy rain, because of contaminants that get washed in from roads, construction sites and who knows where else along with the rain."