The leaves of water hemlock are oblong with jagged edges. The plant produces white blooms that may be confused with Queen Anne's lace. The fading blooms of water hemlock convert to seed that spread by the wind or water to re-establish.
Poisonous if eaten
Ingestion of water hemlock is dangerous for humans and animals. Symptoms of water hemlock poisoning start with vomiting and lead to seizures. The National Institutes of Health states, "The ingestion of water hemlock can lead to serious complications that may be fatal. Prognosis is good, however, if prompt supportive care is provided."
Saw this by the river while hiking. Sure makes for a safe place for geese to shelter.