Schools in the area have been closed since Tuesday as officials try to learn from where the small, red insect larvae came and how long it will take to eliminate them, CNN reported Thursday.
The worms, ranging in length from about a quarter-inch to a half-inch, were found Monday.
While there are no known ill health effects from the worms, local officials said they wanted to err on the side of caution and hand-delivered letters to residents warning them use bottled water until the issue is resolved.
The Oklahoma Department of Environmental Quality was investigating what caused the outbreak in the rural town 75 miles from Tulsa, but hasn't been able to say when the water will be safe to drink, department spokeswoman Erin Hatfield said.
Colcord Water Commissioner Cody Gibby said he is wondering how the worms penetrated the town's water filtering system, CNN said.
"It's not just a little 6-inch filter; it's 6 [feet] of coal and sand mixed together that not even a hair can get through," he told KJRH, Tulsa. "And these worms are getting through it and getting into our distribution water."
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