Donya was fishing in Pickwick Lake in northwest Alabama on June 11 when she encountered a strangle ripple occurring on the water with no visible cause. Donya said they had never encountered such a phenomenon before after years of fishing in the lake.

Local media quoted an explanation from Hardin County Emergency Management, which called the effect a “warm water discharge.” The discharge occurs when warm water from an industry is sent back into the river. Credit: Donya Briggs Scott via Storyful