Daughter of the Deep by Rick Riordan

Royal Format. Pre-loved. A BRAVE NEW HERO. ANOTHER LEAGUE OF ADVENTURE. Generations of Ana Dakkar's family have attended the legendary Harding-Pencroft Academy, where the best underwater explorers in the world go to train. When Ana witnesses a tragedy, her life at school and beyond is changed forever. It turns out that Harding-Pencroft and its rival school, Land Institute, have been fighting a cold war for a hundred and fifty years - and it's just turned hot. Pursued by enemies, Ana learns her family's ties with Harding-Pencroft go deeper than she ever imagined - back to her not-so-fictional ancestor, the legendary Captain Nemo. Land Institute will stop at nothing to acquire the secrets of Nemo's technological genius. Only Ana and her class of half-trained future explorers stand against them. And with her enemies seemingly always one step ahead, can Ana trust anyone but herself...?