Furies are present in almost every body of water deeper than a puddle; they will normally simply circle around. The strain are invincible and if Nathan Hale comes in contact with one, he is automatically killed, the Fury grabbing and biting him. In general they are used to render bodies of water as instant death traps, though sometimes the player is asked to quickly swim through Fury-infested water. When seeing water, it is advisable to search the area for Furies before trying to swim through it.
Furies makes a minor cameo in Resistance 3, being seen frozen underneath a frozen lake in Central Park in New York City. It is imply that the Furies had somewhat participated in the defense of the city's Chimeran tower from SRPA forces but were eventually caught frozen in the water caused by the Chimera's terraformation process.
The Fury's name is derived from the Furies, or Erinyes from Greek mythology in which they are female deities of vengeance or supernatural personifications of the anger of the dead.
Furies strongly resemble to the giant fishes in Ratchet & Clank (also developed by Insomniac) who also instantly kill the player if they should venture too long in the water.
In Chicago a Fury is seem to briefly climb up onto a car before re-entering the water, resembling a seal. It is unclear to what extent these creatures can move around on land, though since they never attack the player while they are climbing on other cars, it is doubtful they are particularly effective there.
Despite being impossible to kill in Resistance 2 (even with Pulse Cannon or LAARK fire) Nathan Hale easily kills a Fury in Resistance: The Gathering Storm with exploding Magnum rounds. It is unclear whether this means Furies being impossible to kill is a gameplay conceit or the book is in error in showing them as killable.
Furies are mentioned but never seen in Resistance: Burning Skies in the intel document "Strange Shellfish". The intel details a fisherman to a friend writing about how he caught a large "shellfish" that is about 7-8 feet long.