An area that is both part land and part water.
Hydrology is usually the least exact of the three parameters.
Indicators of wetland hydrology are sometimes difficult to find in the field. One detail that must be stressed concerning wetland hydrology is that an area does not have to be wet year-round to be considered a wetland. Some areas may contain moisture for several weeks or months out of every year, or they may stay dry for years on end. When the soil is visibly saturated or inundated with water, the presence of a wetland hydrologic regime can be relatively easy to discern. When the area does not exhibit standing water, however, identifying wetland hydrologic conditions becomes more difficult.