An underwater police search team was scouring the river in Taunton for an 89-year-old man who went missing in the early hours of Friday.
Police launched an appeal after Peter Carver went missing. They described him as vulnerable.
Carver was thought to be wearing slippers and a light-coloured quilted gilet or waistcoat. He had a large plaster on the right side of his head.
Police said he may have appeared confused or depressed and may not have taken his required medication.
He was said to regularly walk around Taunton town centre and it was thought he could have been sheltering from the cold weather in a shop, a shed or a garage.
However, they are now searching the river after CCTV footage showed a man, matching Carver's description, wading into the water.
A police statement said: "We can confirm that we have turned our attention to the river in Taunton.
"We have CCTV coverage showing a man matching the description of our missing person waded into the river.
"We started a search in an around the river using our underwater search team with assistance from the fire service's rescue boat and assistance from search and rescue teams.
"The search will continue as long as possible this evening and then continue tomorrow."