We had to wade through waist-deep water to get to the hives.
"Some of them weighted probably 90 to 100 kilos with the the frames, honey and bees inside, and when you throw in the water it's quite heavy."
Mr O'Brien said it took about two hours to move four hives to higher ground at the Exeter Street garden.
Happy with their efforts, Mr O'Brien and Mr Cooper took a rest.
But by 9pm, they had to head to the garden again - the next row of hives were completely inundated.
"This time we were shoulder-deep in water," Mr O'Brien said.
"There was one that we couldn't move. But then we were able to get it out, because the water had lifted the hive up and the air trapped inside allowed Steve and Simon to float it out of the enclosure."
Mr O'Brien said they trio managed to save 19 out of 21 hives, and some of them needed to be moved more than once to higher ground as the waters kept rising.
"It was definitely an ordeal," Mr O'Brien said.
"I left there just after 12am and Steve finished at 1am. He went back down at 3am because some of the hives hadn't been moved high enough.
"It was a crazy night and I've copped numerous stings after getting about two dozen bees inside my suit.
"Steve doesn't wear gloves, so he's a bit sore and sorry today."