In aquatic habitats they overlap with the Pseudomonadaceae in their ecology, although pseudomonads favor fresh water and vibrios prefer salt water. The genus Vibrio contains an important pathogen of humans, Cholera. Cholera is an intestinal disease with a pathology related to diarrheal diseases caused by the enteric bacteria. The overall conversion of NH3 to NO3 is called nitrification. Some diplomonads are free-living and may be common in stagnant fresh water, but most are commensal in the intestines of animals ii.
Most known euglenids live in shallow freshwater iv.
Thus definition by taxonomy is not useful. At our current state of knowledge, the term freshwater ascomycete refers to an ascomycete that occurs on submerged substrata or on submerged parts of partially submerged substrata located in aquatic habitats.