Optical cable with optical fibers and a water blocking element extending together along a passageway. The water blocking element swells upon contact with water so as to block the passageway against water migration. The water blocking element may be of filamentary structure, e.g. string or tape which acts as a carrier for water swellable particles, e.g. polyacrylate. The water blocking element may, however, be a filament of the swellable material which is spun with other filaments, e.g. polyester to form a string. The cable may be air pressurizable.