The building of the canals took an enormous cost in human lives. It is eloquently described in Solzhenitsyn - Gulag Archipelago. The ultimate and tragic irony is that the canals proved useless for commerce. there is also a series of famous photos of Stalin, Voroshilov, Molotov and Yezhov inspecting the canal. After his purge, Yezhov vanishes into thin air in subsequent versions of the photo.
It is imporant to keep in mind that this is not an NKVD badge. It is a badge that was issued to NKVD personnel and many other types of personnel including those from construction, railway, inland waterways commissariats and other specialists involved in the project.
Some dealers try to call it an official NKVD badge which it is not.