The bravery of a bystander who dived into a freezing Christchurch lake to try to save a husband and wife who drowned after a driving lesson turned to tragedy has been commended by a coroner.

Avneel Ram, 26, and his 31-year-old wife Sheetal died after she accidentally drove into the lake in the Halswell area of Westlake Reserve on September 12 last year.

In findings released today, coroner David Robinson ruled they both drowned as the result of an accident, and made no recommendations over the circumstances of their deaths.

The Rams, from Fiji, lived in Christchurch with their 6-month-old daughter.

Avneel Ram operated an air-conditioning company with a close mate.

The coroner noted that Sheetal Ram had decided to try and get her drivers' licence, and passed her learners test in August last year.

She had tried to learn to drive in Fiji about six years earlier, the coroner heard, but had "suddenly accelerated and hit the leg of a kerosene tank" and had not driven since.

Two days before the Christchurch tragedy, her husband had bought a red Toyota Cynos for her to learn in.

On Tuesday, September 12 last year they went to Westlake Reserve for a lesson.

Several witnesses saw Avneel Ram standing outside the car in the carpark, talking to his wife who was sitting in the car, the coroner said. All the windows were up.

She started the car and then drove over the carpark curb and onto the grass slope towards the lake.

Witnesses described the car accelerating down the slope and entering the lake without braking.

Avneel Ram went into the water, chasing after the car.

The coroner noted that neither her or his wife were competent swimmers.

A member of the public, who had been walking around the lake, grabbed a rock with the intention of breaking a window to help get Sheetal Ram out of the car.

She entered the water to help, the coroner said, but turned back as she was not a confident swimmer either. Nobody else entered the water.

The car stayed afloat for a while and Avneel Ram was seen holding on to it.

After it sank, Ram dived down after it.

He resurfaced several times for air but eventually failed to come back up.

Emergency services arrived and members of the Fire Service entered the lake on safety lines with breathing apparatus. Police staff also entered the water and tried to help.

The water was "very cold" and visibility poor, the coroner found.

Neither the car or the Rams were found and after about 30 minutes it was acknowledged that they would not have survived and the search was called off for the night.

The car was found the next morning by members of the Police Dive Squad at a depth of 2.8 metres and their bodies were recovered. Distraught family members and friends formed a guard of honour, crying and hugging, as the bodies were taken from the lakeside into the back of a waiting hearse.

Forensic pathologist Martin Sage concluded they had both drowned.

Coroner Robinson agreed and ruled their deaths accidental.

He commended "those who made attempts to rescue the pair".

Evidence from two witnesses "somewhat distant from the scene" that the Rams had been arguing before the accident was discounted by the coroner.

Sheetal's brother-in-law Hinesh Kumar earlier said Avneel was a "hero" for trying to save his wife.

"He is a hero to us. He tried to save his wife. Not everyone would do that," Kumar said.

He described the couple as "very friendly, very happy people".

"They were really fun to be around, really nice," Kumar said.