Crews treating for poisonous water hemlock at White Rock Lake

DALLAS (CBSDFW.COM) — Spotted growing along the shoreline at Dallas' White Rock Lake? Poisonous water hemlock.

"The entire plant is toxic," explains Urban Biologist Brett Johnson with Dallas Parks & Recreation.  "[It contains an] extremely strong convulsant and people that have ingested it have died from it. We have never had that happen here and if you look at the statistics it's a very minor issue... but because we are in such an actively used park, we wanted to make sure it was taken care of."

Initially spotted by a nature savvy visitor, that guest alerted city staff.  Johnson says the plant is too toxic to mow or remove by hand, so trained crews are applying an herbicide approved for use near the water to individual plants.

"Treating it now, we can keep it from going to seed production," explains Johnson.

Hours after the herbicide was applied Friday morning, some plants were already beginning to yellow.  Still, Johnsons says it will take 2-3 weeks for the plants to die.  The level of toxicity will decrease over that time.  But, for now the message to remember: just stay away — a message that Johnson continued to share with visitors who'd heard about the poisonous weed.

"I think it's great that he could answer that," says a park guest who approached Johnson to ask questions, "so I will avoid the bushes and just be on the grass."

According to Johnson, the poisonous water hemlock isn't toxic for waterfowl, so that's likely how the seeds were spread.  Skin contact will likely only be an irritant. However.  If ingested the poisonous hemlock could kill within a matter of minutes. Call local poison control if concerned about accidental exposure. Bottom line?

"Stay on the trail," says Johnson.  "Don't eat it and you're good."