The council pleaded guilty to three health and safety breaches following the death of Emma Farrar on November 13, 2001.
Emma, a pupil at Park school in Blackpool, was found floating face down in the water after a half-hour swimming lesson with 10 other pupils in the pool of neighbouring Woodlands school.
Pauline Mills, 55, a swimming teacher, of Newton, near Kirkham in Lancashire, was cleared of manslaughter two weeks ago.
Blackpool council pleaded guilty to not giving proper guidance to staff as to when to leave the swimming lesson, having no system in place to properly monitor training and having no system to ensure staff had relevant medical information.
Steve Weaver, chief executive, said the council had now taken the "unprecedented" step of having a qualified lifeguard as well as teachers and swimming teachers at swimming lessons.
He expressed the council's deepest sympathy to Emma's family and said that, following the case, it would also conduct an internal investigation into the incident.