Connie Bakken made the discovery when she looked outside her bedroom window.

"I called my husband and said: 'Why is the stream purple?'" she told CNN.

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"It actually looked like purple paint."

The couple alerted authorities who intervened to avoid the purple creek contaminating a nearby lake.

They believe someone poured a substance down a storm drain, which resulted in the discolouration.

Officials then went door-to-door questioning locals about the incident.