back swamp; back marsh; back slough
Geological term for a low-lying, poorly drained area behind a natural levee, often found in floodplains.
A back swamp is a marshy area formed behind a natural levee.
Compound of 後背 (kōhai, 'rear, back') and 湿地 (shitchi, 'wetland, marsh'). The term is a direct calque from English 'back swamp' or 'back marsh'.