The four-year-old Jack Russell was frightened by the thunder and lightning and owner Jamie reckons he went into hiding.
"He disappeared but there was no rain at that stage. I thought he'd come back on his own when things calmed down.
"I was sitting eating a bowl of cornflakes when the river's bank burst and water started coming in the door. My downstairs was flooded."
Jamie said he couldn't find Rusty the day after and fears the rescue dog was washed away by the strong currents.
"There hasn't been a trace of him. I thought I'd find him regardless whether he is alive or dead. I'd hate to think he's lying somewhere injured. The current was so strong. I don't know what happened to him."
Anyone who has seen Rusty is urged to get in contact with Jamie on 0857895064.