The fiancee, Lindsay Grennan, told KOMO News she and Johnny Sharrar threw a stick in the water and then the trouble started. The dog got caught in a strong current and the couple frantically jumped in to save the dog.
"I was trying to stay afloat the best way that I could and yell at him to try to stay afloat," Grennan said, "to try and get on his back and float. And he couldn't do it."
A diver rescued Grennan and the dog got out OK.
A King County Sheriff's chopper flew up and down the river searching for Sharrar, and on the ground, a dive team looked in the murky, cold, water.
The current is so strong, rescue boats are even having a tough time going upstream at full throttle.
Rescuers say that if you're dog goes in the water, do not jump in to get him because they say most dogs can swim right back to safety.
"More often than not, we see people go in after their dogs and then the dogs make their way out and people don't," said Charlie Ajkers, a diver with the King County Sheriff's office.
While crews search, Grennan hopes they find her fiance -- she's pregnant with their child and wants a sense of closure.
"I love him more than anything in this world and I don't know what I'm going to do without him," she said. "I'm just praying that there is a miracle."