The silver Ford Ranger ute, registration HKD553, that she is believed to have been driving, has not been found.
Waikato Detective Senior Sergeant Ross Patterson previously said the national dive squad was searching areas of the lake "that require further investigation".
"Waikato Search and Rescue Team and investigators are also on site, working together during this phase," he said.
"Despite our extensive inquiry we still hope to find her, though we now believe she is dead.
"We are still keen to hear from anyone who has information relating to Kim's disappearance, as we are committed to bringing her family closure."
Thirteen dive staff were carrying out the search on parts of the 9sq km lake with support from police, a harbourmaster vessel and Mercury Energy craft.
The hydro-electric generator at Arapuni was shut down to provide a window to search the causeway this morning.
The search would continue this afternoon and return tomorrow if necessary.
Richmond and her partner Corey Jefferies had been at a social at the Arohena Hall on the night of July 30 to watch the Chiefs versus the Hurricanes Super Rugby semifinal.
Jefferies was the last out of the hall, about 10.30pm, and as one of the trusted members of the community who had a key, he locked up the building on Pukewhau Rd.
The couple drove back along the winding rural road to their Mangare Rd home where it's believed Jefferies and Richmond, dressed in a Highlanders jersey, watched the second semifinal in the wee hours of July 31, between the Highlanders and the Lions.
It's not clear why, but some time later Richmond drove off in her ute.
The 42-year-old mother-of-three hasn't been seen since.
Richmond, a former Bay of Plenty table tennis champion who was mad on sports and had been competing in triathlons for two years, was a devoted mum. She was fit and strong, despite suffering severe hearing loss in recent years.
By all accounts she and Jefferies were a "normal" couple.
Described as happy and hard-working they were heavily involved in the community and highly regarded by other Arohena residents.
No one can explain the disappearance and her whereabouts remain a mystery, despite a massive search by police, land search and rescue, the police Eagle helicopter, a specialist dive squad who searched a lowered Lake Arapuni, Richmond's extended family and dozens of people from the community.
No clues were found. To make matters worse it was freezing cold on the night, with howling wind and rain.
Anyone with information about Kim Richmond's disappearance is asked to contact Acting Detective Sergeant Ian Foster or Patterson at the Te Awamutu Police Station on (07) 8720 100 on Crimestoppers on 0800 555 111.
