Gazprom claims that Nord Stream pipes are filled with water "for hundreds of kilometers" 

This is reported by RBC.

"We have not yet been allowed to the site of the accident, but we must understand that the speed with which the gas pipelines lost pressure makes it clear that a complete rupture of the pipe occurred. What does this mean? It means that the pipe for a very long distance now, in particular towards Russia,  is filled with seawater... Experts say that to restore work after such a terrorist act, you have to actually cut off a large piece of pipe over a long distance and actually build a new section," he said.

If the damaged pipe is to be restored, it must be raised to the surface, which is complicated by its filling with seawater for hundreds of kilometers, Miller emphasized.