A West Australian energy utility has been fined more than $100,000 over the electrocution of a teenager in Geraldton.

Amber Finch, 17, was walking home with friends at night in January, 2011 when she came into contact with a fallen power line which had been brought down during a storm the night before.

Two of her friends were injured when they went to her assistance.

The Geraldton Magistrate's court was told the wires were extremely old and had not been properly maintained.

Western Power pleaded guilty to failing to keep its network safe.

Its CEO Paul Italiano has apologised for Miss Finch's death.

"Western Power accepts full responsibility for its role in, and the assets, that contributed to this fatality," he said.

The company was fined $101,000 and ordered to pay costs.

The magistrate said the utility avoided the maximum penalty of $250,000 because it pleaded guilty at the earliest opportunity.