The vessel had sailed from Barreiro and was preparing to dock at Terreiro do Paço when it crashed into the quayside.
Lisbon Port captain José Isabel said an inadequate speed coupled with poor visibility due to fog could be to blame for the accident.
He added most of the injuries occurred “as people were standing instead of sitting down in their seats, putting them in vulnerable positions which resulted in them being projected.”
Speaking to newspaper Público, José Isabel also said the boat was travelling at “excessive speed” and admitted “fog is one of the situations that causes this type of crash.” He said poor visibility could have contributed to the boat’s captain miscalculating the distance between the ship and the quay.