Marsh arrowgrass can grow in saline conditions, but doesn't tolerate salt as much as its family member sea arrowgrass. It grows vertically out of the ground, its flowers are spread further apart along the stem and it doesn't form the clusters that sea arrowgrass makes. It can be found along the banks of ditches, along (brackish) ditches and in damp hay-fields and sometimes even in tremulous peat grounds. It is found in the dunes in wet valleys. On beach plains surrounded by dunes, marsh arrow-grass is especially found in the border regions between salt and fresh water.