"While snorkelling at Lake Rotoma a student suffered a medical event and was attended to by St John's ambulance. We are deeply saddened to inform you that the student has since passed."
All other students involved were safe and returned to school. They were now being supported by whānau, school staff and a counselling team.
"This is an extremely distressing time for both our students and staff."
The school would be closed tomorrow "due to this tragic event".
Tuhoro offered contact details for counselling and support services for both students and their parents and caregivers.
A police spokeswoman said earlier today officers were called to the scene on Matahi Rd off SH30 along with St John.
One person was in a serious condition with medical assistance being provided.
A St John spokeswoman said staff were called out at 10.45am and two ambulances and one helicopter were at the scene.