Two Tory MPs have raised fears that the HS2 rail line will increase the risk of flooding for homes along its route.
Europe Minister David Lidington said the project would involve building on farmland which currently acts as natural flood protection for homes.
Former cabinet minister Cheryl Gillan said it was "totally unsatisfactory" that a full assessment of the flood risk had not been carried out.
HS2 said it would continue to carry out inspections along the planned route.
A spokesman said the proposed high-speed rail route from London to Birmingham, Manchester and Leeds would be designed to remain operational during a one-in-1,000-year flood.
"Put simply, that means the railway is being built so that it can withstand just the sort of extreme weather that we have seen up and down the country recently," he said.
HS2 did not directly address concerns that the project could endanger nearby properties.
Mr Lidington, the MP for Aylesbury in Buckinghamshire, said in a letter to Transport Secretary Patrick McLoughlin that the Willows area of the town, which is close to the HS2 route, was flooded.
"You will not be surprised to hear the residents are very fearful that the construction and operation of HS2 across the floodplain close to their homes will add significantly to the flood risk," he wrote.
"It is indisputable that both construction and operation will require farmland to be taken which for now soaks up surface water and which ought to act as natural flood protection for my constituents.
"People in this part of Aylesbury are sceptical about the assurances from HS2 that they will design in effective flood protection measures."
'Really big re-development'
Mrs Gillan, who represents Chesham and Amersham, also in Buckinghamshire, said the scale of HS2 amounted to the same footprint as "many, many houses" in flood-prone areas.
"You begin to worry what the risks associated with this development are," she said.
"You would have thought that [a flood risk assessment] was a basic part of any environmental investigation."
Construction on the London-West Midlands phase is expected to begin in 2017 and be completed in 2026.
The onward legs to Manchester and Leeds could start being built in the middle of the next decade, with the line open by 2032-33.
On Friday, Chancellor George Osborne said planners should consider a "really big re-development of Euston" station in London, where the line will terminate, instead of the existing scaled-back plan.