The work, which has been funded by the Agency, Gwynedd Council, the Welsh Assembly Government and EU Objective One money, will eventually mean that 450 homes and businesses in Bangor will be less likely to be flooded from the Afon Adda.
Keith Ashcroft, the Agency's Area Manager for north Wales said: 'This scheme is a huge piece of work but it will make a difference to people living here. The culvert carrying the Adda is quite old and it needed to be upgraded to cope with heavy rainfall. However, while we can reduce the risk of flooding, people still need to prepare themselves and their property. The flooding we have seen this summer shows that extreme rainfall can cause huge problems.'