The Tuolumne River near Empire in Stanislaus County had a swath of hyacinth 300 yards long and 40 yards wide atop the water that cut off any boating.
Seventh grade teacher Elias Ruiz along with a few friends donned scuba gear and made several trips to remove pylons and logs that remained from an old bridge.
They trapped the hyacinth so it couldn't move further down river.
Ruiz says hyacinth is a bigger problem this year because the winter was so mild.
"The plant doesn't die so it persists in the river and as soon as the temperatures warm up in the spring, it starts to multiply so this early in the year it was kind of surprising to see that much hyacinth in one location."
Ruiz says the state is spraying now to kill hyacinth in the Delta but not in the Tuolumne River.
He says he expects the hyacinth to be a bigger problem in the Tuolumne as the summer heats up.