Three years ago, Sonoma County declared war on ludwigia, a fast-spreading plant that was clogging west county waterways and providing safe harbor for West Nile-carrying mosquitoes to breed.

Five years after the end of a $2.1 million campaign to attack it, the invasive aquatic weed Ludwigia once more is clogging Sonoma County waterways. "It's back and it's as bad as ever," said Erik ...