Western water hemlock is a highly toxic member of the Parsnip Family. Western water hemlock is found in sloughs, wet meadows, along streams, and other wet areas. This plant is poisonous to all types of livestock and to humans.

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Leaves are alternate, compound, twice or thrice divided, with petioles that partially sheath the stem. Stems are erect and solitary. Stems are hollow and smooth, branching, swollen at the base, and purple-striped or mottled. Flowers are white and compounded, flat-topped, umbrella-like clusters at the ends of stems and branches.