There are three defining characteristics of a wetland. These characteristics can be used as indicators to define a wetland ecosystem. The three characteristics/indicators include:

1. Hydric Soil: In Ontario there are two main characteristics of hydric soils. Scientists also refer to hydric soils as aquic condition -- the condition in which soils are saturated with water, are reduced, and display specific characteristics that allow for their identification (the characteristics are collectively called redoximorphic features).
2. Hydrophytic Plants: Hydrophytic plants are water-loving plants that are specially adapted to growing in saturated or periodically saturated soil. This is the most reliable indicator of a wetland ecosystem because plants have specific growing requirements that must be met or they will be succeeded by more terrestrial plant species. There are two types of wetland plants, obligate species (plants that grow exclusively in wetlands) and facultative species (plants that most often occur in wetlands, but not exclusively).
3. Hydrology: Hydrology refers to the presence of water and or saturated soils whether permanent or periodic for one week or more. Some wetlands are dry for most of the year, so use this indicator with caution.