bog - quagmire - swamp - reservoir
bog ciénaga, pantano [soft, wet ground]: The water level in the bog varies only a few inches during the year.
boggy pantanoso,-sa: a boggy patch
quagmire /ˈkwɒgmaɪə, ˈkwæg-/ ciénaga [similar to bog, and you sink into it when you walk on it]: The streets were a quagmire of mud and manure.
swamp /swɒmp/ pantano [an area covered with water]: I was lost in an alligator-infested swamp. ^ The swamp stretched out for miles.
reservoir /ˈrezəvwɑː/ pantano [natural or artificial, for water supply to the population]: The water piped from the reservoir was so polluted and sullied that it was of little use.