Endothall is a selective contact herbicide that has been used to manage submerged aquatic vegetation for over 50 years.

[5] It is considered safe in drinking water by the EPA up to a maximum contaminant level of 0.1 mg/L (100 ppb).

Some people who drink water contaminated above this level for many years experience stomach or intestine problems.

[8] There is limited data on human toxicity, although cases of lethal deliberate self-poisoning have been reported with as little as a mouthful of Endothall concentrate.

[9][10][11] Features of toxicity include corrosive injury to the oropharynx and gastrointestinal tract, metabolic acidosis, coagulopathy, and multi-organ failure.