An infamous graffiti tagger has defaced a 30-year-old mural depicting Northcote women so badly it is probably beyond saving.

The giant artwork at the Gas and Fuel depot wall on the corner of Hodgkinson Street and Smith Street was painted in 1986 by Melbourne artists Eve Glenn and Megan Evans.

The historic Northcote mural after being tagged by Nost. Credit:Joe Armao

But last month the notorious graffiti artist known as NOST "capped" the work, putting his own tag over it.

City of Yarra mayor Roberto Colanzi said the mural was so badly damaged that it probably could not be saved.