The water hemlock (Cicuta virosa) can grow up to 1.5 metres tall and is considered one of the most poisonous species in Finland.
Open image viewer
Despite common misconceptions, water hemlock is not an invasive species. Image: Emma Nordblad / Yle
A highly toxic native plant, the water hemlock (Cicuta virosa), has been spotted at popular swimming spots across Finland and led to warnings from authorities about its dangers.
Sightings of the plant have been made in Ähtäri, Lehtimäki, Salla and Oulu, with locals sharing alerts via social media and neighbourhood forums.
The plant, which blooms in July and August, can grow up to 1.5 metres tall and is considered one of the most poisonous species in Finland.
Despite common misconceptions, water hemlock is not an invasive species.
“Water hemlock is a Finnish plant and can be quite common in certain areas, especially along wet shorelines by lakes and rivers,” said Markus Seppälä, a conservation specialist at the South Ostrobothnia ELY Centre.
“It’s most prevalent in southwest and western Finland, but rarer further north.”
Seppälä, who advises on invasive species in the INSPIRE project, said the plant often causes confusion.
“I get calls about it regularly from people who assume it’s invasive,” he said.
Toxicity risk to swimmers and livestock
The danger lies in the plant’s toxin, cicutoxin, which is present in all parts of the plant—most potently in the root system.
“The plant is poisonous even on contact, but particularly hazardous if the root is broken or disturbed,” Seppälä explained.
“Breaking or pulling the plant can release toxins into the water, posing a risk to swimmers and livestock drinking from the shoreline.”
Seppälä emphasised that the plant only releases toxins when handled or damaged.
Ingesting water hemlock can trigger severe symptoms, including vomiting, convulsions, and frothy salivation. In the worst cases, poisoning can be fatal.
Often mistaken for edible plants
Water hemlock closely resembles other harmless umbellifers, such as cow parsley and ground elder — plants that are sometimes harvested for food.
“It’s crucial to follow the same rule as with mushrooms: only pick what you can identify with certainty,” said Seppälä. “Mistaking water hemlock can be deadly.”
He recommended reporting sightings at public swimming areas directly to local authorities, who are usually quick to respond and remove the plant. Proper removal requires protective gear.
“It’s important to notify swimmers of eradication efforts and avoid entering the water near the site until any toxins have had time to dilute,” Seppälä advised.
He also urged people to teach children how to recognise the plant.
“Accurate knowledge about the dangers and how to identify water hemlock helps prevent accidents.”