The little girl was reported missing at 1.30pm.
Tamar's parents and other family joined neighbours, friends, police, search and rescue and Coastguard staff to scour the area.
Mr Foster said searchers looked "everywhere" for Tamar, including the river and the Helensville township - about 1km north of her home.
Her father found her just after 5pm in thick mud at the bottom of the jetty, about 50m from the front door of their home.
Mr Foster said it was just on low tide when she was found. Tamar's father carried her home. There was no hope of resuscitating her.
The family gathered at the house yesterday.
"They're not good," said Mr Foster. "The whole family are beside themselves, blaming themselves."
Tamar's death will be referred to the coroner.
The tragedy brings this year's drowning toll to 114, compared with 80 at the same time last year.
Water Safety New Zealand chief executive Matt Claridge said there were two important things for parents to keep their children safe.
"Firstly that access to the water is isolated, so a fence in front of a pool, keeping the bathroom door shut and properties fully fenced.
"And the second one is that parents' supervision needs to be active and constant. So that means when kids are around water, mum and dad should be in or around the water themselves."
While 90 per cent of drownings among pre-school aged children are in or around the home, this year the number of children who had wandered off and drowned had risen steeply, Mr Claridge said. "That just comes back to supervision."
