Endothall

Endothall is a contact aquatic herbicide labeled for hydrilla, pondweeds, and Eurasian watermilfoil. Faster-acting than fluridone (visible effects in 7–14 days) and commonly used as a rescue treatment when fluridone fails or hasn't been started in time. Damages most submerged native vegetation at labeled rates. Two formulations: dipotassium salt (lower aquatic toxicity) and the alkylamine salt (more potent but more toxic to fish).