Work to further improve flood defences on the tidal stretch of the River Clwyd has begun, 20 years since communities were hit by floods.
Environment Agency Wales said 1,150 homes and firms in Kinmel Bay and Rhyl were at risk from a major flood.
The embankments on the Clwyd from Rhyl to Rhuddlan, both in Denbighshire, were continuing to sink into peat.
But the agency said the work "will not resolve the long-term issue" of the flood risk on the flood plain.
In 1990, the coastal communities of Kinmel Bay and Towyn, in Conwy, were devastated by floods.
Flood defences were topped up to the required height in 1991.
The agency said that if the new flood defence work was not carried out, then within 10 years the number of homes at risk would more than double to 2,760.
The building work, costing £500,000, is on both sides of the river and is to continue into the autumn.
Meic Davies, flood risk manager for north Wales, said: "The area is at significant risk from tidal flooding and this project will help to reduce the danger caused by the embankments sinking into the peat."
The assembly government is partly funding the scheme, which includes monitoring the banks, and increasing them as required, for the next decade.
However, the agency said the increased protection could only be a temporary meausure for the next 10-15 years in the face of climate change, rising sea levels and the continued sinking of the new banks.
He said: "It's important to emphasise that this will not resolve the long-term issue of how we deal with the flood risk in this flood plain.
Mr Davies said the agency was putting the finishing touches to its proposals for a long-term flood strategy for the area which it would present "in the next few weeks".