Experts say it would cost £4 million to save Malton and Norton from another disastrous flood - and £1.3 million to protect Pickering.
Consultants have suggested a scheme to prevent the River Derwent bursting its banks and flooding homes in Malton, Old Malton and Norton.
The Environment Agency, which commissioned a study by the consultants, says a system of "hard and soft" defences -flood walls and grass banks - is being recommended at an estimated cost of £4 million.
A spokeswoman said today that it had been estimated that another flood would cost the towns £17 million.
Up to 200 properties would be at risk, with additional disruption to highways and railways, and distress and anxiety.
A separate scheme, costing £1.3 million, to protect up to 40 Pickering properties and the A170 main road from flooding by the town beck, has been suggested by consultants.
The EA says the scheme would include raising banks and possibly flood walls.
The agency stressed today it could be another ten months before Environment Agency officers have fully assessed both sets of proposals, and are able to recommend to the Yorkshire Regional Flood Defence Committee whether they should go ahead.
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