This is the 11694th most frequent Russian word.
заболоченной
Marshy or swampy.
Заболоченной is used as an adjective describing 'низиной' (lowland), indicating its swampy nature.
Лес вокруг был заболоченной низиной.
The forest around was a swampy lowland.
Заболоченной is used as an adjective describing 'тропинка' (path), showing that the path became covered with or resembling a swamp.
После дождей тропинка стала заболоченной.
After the rains, the path became swampy.
Заболоченной is used as an adjective describing 'местности' (area), denoting that the area had characteristics of being swampy.