A woman who killed her three youngest children by deliberately driving her car into a lake, in what a Supreme Court judge described as a "horrendous crime", has been jailed for 26 years and six months.

But Justice Lex Lasry ruled on Tuesday that Akon Guode's life was in turmoil on April 8, 2015, when she drove into Lake Gladman in Wyndham Vale with four of her children in the car, and that there was a connection between her disturbed mental state and the offending.

Guode drove four laps of the lake before she did a U-turn, steered through the only entry point to the lake and accelerated into deeper water.

She then got out but did nothing to help residents and emergency services workers who frantically tried to save the children.