The celebrity chef rushed to save his sister Jacqueline when she tripped and fell into the water at the event in May this year, with photos showing him lifting her out.
He has now spoken out about the incident, telling the Daily Mail: "The Health and Safety was not particularly great.
"They should have roped it (the pond) off."
Harriott, who was speaking at the TRIC Awards, said the water feature was around 6ft deep.
"Quite a drop once you hit the water," said the 65-year-old.
Jacqueline had been her brother's guest at the event and was among those admiring the Our Green Planet and RHS Bee Garden exhibit when she stepped backwards and fell into the pond, with onlookers saying that she was completely submerged.
The Ready Steady Cook star later updated fans on Twitter and thanked everyone who had helped his sister, who is a retired teacher.
"She’s doing fine and all is well," he tweeted.
The Royal Horticultural Society (RHS) told Yahoo in a statement: “We take health and safety very seriously across the RHS, and onsite medical professionals attended to the incident at the RHS Chelsea Flower Show press day within two minutes.
“After their rapid response, we were pleased to hear that the guest left the Show and made their own way home and was well.
“Throughout the remainder of the Show it was decided as a precaution to not allow public access on the garden.”
Yahoo has contacted a representative for Harriott for comment.
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