Six people were also injured in this accident.
The accident took place around 7.00am in Bahaddarhat area under Sitakunda upazila. Passengers of the microbus were going to attend a namaz-e-janaza.
The deceased were identified as micro passengers Md. Naser (60), Md. Solaiman (51) and local resident (pedestrian) Monika (47).
Chittagong Kumira Highway police outpost in-charge Muniruzzaman said that the microbus fell into the pond after losing its control.
The injured were admitted to Chittagong Medical College Hospital for treatment.