Water Hag

Water Hag was a term humans used to describe an advanced race of alien creature native to the planet Strepto.

Biology
Water Hags were humanoid in basic appearance. Their skin was emaciated and the colour of mud and their eyes were yellow with black slits for pupils. They had extremely wide mouths filled with sharp teeth, capable of easily biting the head off a dog. They had talons "as hard as iron" instead of fingernails, which were sharp enough to slice someone in half and even carve out solid rock. This killing method was a characteristic marker of a Water Hag killing. Despite their savage attitude, they were intelligent as (and possibly even more than) a human and the ones led by Sally Blackteeth were able to navigate the rift through unknown means. Water Hags weren't entirely animals, also having vegetable traits (giving them weed-like hair and bark-like skin).

Water Hags possessed many superhuman abilities, even from birth, that made them difficult to evade or kill. They could disguise themselves as human, had strength superior to a human's, were incredibly quick (to the point where their motion became highly blurred to the human eye), could fly using a cloud of water, had the ability to breathe both underwater and on land and could possibly dissolve into water.

Life cycle
The Water Hags appeared to be a female-only species, and their only method of procreation was to infect humans with a virus of sorts.

This "virus" acted in the oesophagus, where it caused the development of a foetus-like organism made of phlegm and vegetable matter. At this stage, the creature was called a "Homunculus" and until maturity it would incubate and grow in the throat. As the organism grew, the host would develop a cough, then become weaker and weaker. Eventually, the host would die, then briefly reanimate (this could occur as much as 40 years after the death, depending on circumstances and preservation). At this point, the Homunculus would attempt to extract testosterone from the host in order to catalyse its growth. If it succeeded, it would burst forth from its host's throat. They could then reach maturity to Water Hag form within a day.

However, if the Homunculus did not get the required amount of testosterone, then during the host's short spell of unconsciousness, the Homunculus would die and be vomited by the host, "stillborn" as it were. This meant that it was nigh on impossible for the homunculus to procreate inside a female human unless it injected with testosterone. Likewise, if the Homunculus chose a male host and that host was injected with a mix of oestrogen, emetics and antibiotics, then the parasite would die and be thrown up. (PROSE: Something in the Water)

History
At some point during the Middle Ages, (PROSE: Something in the Water) Strepto was stolen by the Daleks. (REF: The Time Traveller's Almanac) One Water Hag, later known as Sally Blackteeth, had been off planet at the time and was able to escape to Earth with the Cardiff Space-Time Rift. She planned to replenish her people and infected humans with the virus. She and her offspring were spotted throughout history, creating the legends of the Water Hags.

In 2009, Sally took the name "Saskia Harden" and faked a suicide. With her being brought to the hospital, it allowed her to infect more people. Torchwood began to investigate, but they too became infected. Sally and her children then attacked Torchwood itself, but they were able to hold them off. When Sally tried to escape through the Rift, Jack Harkness followed her and pulled her back, weakening her and allowing the rest of Torchwood to kill her. With her death in the Rift, the other Water Hags were destroyed. (PROSE: Something in the Water)