Yes, Water Hemlock is toxic to dogs!
Dogs accidentally consuming the Water Hemlock plants can show the following clinical symptoms: Vomiting, Prolonged Depression, Incoordination, Hypersalivaton, Sleepiness Or Excitation, Dilated Pupils, Low Body Temperature, Low Blood Pressure, Coma, Seizure And Death (In Rare Cases).
Water Hemlock consumption is also toxic to Cats and Horses.
Toxic Principles Of Water Hemlock: Cicutoxin.
More Info About The Water Hemlock Plant
Scientific Name: Cicuta maculata
Family: Apiaceae.
Also known as: cowbane, poison parsnip.
The answer is based on information found on The American Society for the Prevention of Cruelty to Animals (ASPCA) website.