The 'bad' smell of swamps comes mainly from hydrogen sulfide a byproduct (waste) of the microscopic anaerobic bacteria that breaks down dead organic matter. read more
Swamp water smells because of the following reasons. Warm moist environments are idea for algae, bacteria and fungus. Add to that decaying vegetation and you have the smell of a swamp. Microbial Activities that is constantly carried out in the limited water results in the smell. read more