President Bola Tinubu has told the government to route the Lagos Calabar coastal highway through the existing East West road from Ondo into Edo State.
The change also comes after floods hit the East West road, especially near Ughelli in Delta State.
Umahi said the road was built before climate change was fully considered.
Delta Governor Sheriff Oborevwori stepped in over the flooding.
The federal government plans to raise sections of the road by about two metres.
He said the old route ran through deep pits and areas without good sand for building.
Filling works are almost done, with more than 10 metres of sharp sand being added.
He said he has heard about petitions against him but has no regrets.
The changed section covers 67 kilometres, with 27 in Ogun State and about 40 in Ondo State.
The Ondo to Edo corridor, including a 45 kilometre bypass around Benin City, is 104 kilometres long.
Section two, a 55 kilometre dual road ending at the Lagos Ogun border, should be done next month.
At the Calabar end, sections three A and three B are more than 30 percent complete.
Work is also going on in Akwa Ibom State, where a 82 kilometre dual carriageway is being built.
Surveys are underway for a 129 kilometre road from the Edo Delta border to the Delta Bayelsa border, with work set to start in November.