Marais vs. marécage
'Marais' and 'marécage' are French terms that are often used to describe wetland areas. While they are sometimes used interchangeably, they have subtle differences in their meanings and usage which relate to the characteristics of the terrain they describe.
Marais
A marais typically refers to a marsh, which is a type of wetland characterized by grasses, reeds, and other herbaceous plants. Marais may be periodically or permanently saturated with water and can be found in both freshwater and saltwater environments.
Le marais poitevin est souvent appelé la Venise Verte.
(The Poitevin Marsh is often called the Green Venice.)
Les oiseaux migrateurs font une pause dans le marais durant leur long voyage.
(Migratory birds take a break in the marsh during their long journey.)
Marécage
A marécage refers to a swamp or bog, typically featuring standing water along with trees and shrubs. It's usually more waterlogged than a marais and may have a peat base. Marécages can be seen as denser wetlands with woody vegetation.
Il est difficile de marcher dans le marécage à cause du sol boueux et des racines.
(It is difficult to walk in the swamp because of the muddy ground and roots.)
Les marécages sont souvent peuplés par des espèces de reptiles et d'amphibiens.
(Swamps are often populated by species of reptiles and amphibians.)
Summary
In essence, while 'marais' and 'marécage' both refer to wetland ecosystems, 'marais' tends to describe marshes with herbaceous plant life and may be part of coastal landscapes or inland waters, while 'marécage' conveys the idea of a swamp or bog, more frequently associated with muddy waters, dense vegetation like trees and shrubs, and a peat composition commonly found away from coastal areas. Understanding these nuances can aid in depicting these natural environments more accurately.