An NHK survey says in the 6 and a half years since the 2011 earthquake and tsunami, only about a third of the seawalls planned in northeastern Japan have been completed.
The survey found 206 seawalls had been built as of June this year in Miyagi, Iwate and Fukushima prefectures.
The government initially planned to build 602 walls in the affected areas over about 5 years.
While construction is underway at all sites in Iwate and Fukushima, around a fifth of the projects in Miyagi have yet to start.
The prefectures say work has been held up by the time it's taken to purchase the land and by preparatory work.
In some places residents haven't given their consent for the construction.
The government reviews the plan every year and now aims to complete all projects by March 2021.