Prof Walther Schwarzacher, a Bristol University physicist, took Edilamar Prates-Schwarzacher, 43, to see places linked to his childhood in July 2009.
She had an upset stomach and went into woods to relieve herself during a walk, the inquest in Truro heard.
Post-mortem tests showed she had drowned. An open verdict was recorded.
Cornwall's deputy corner Andrew Cox told Truro City Hall there was no hard evidence to say exactly how she had died.
"I could speculate that she went to the toilet, came down to the river to wash her hands and fell in, but it would be complete speculation and there is no evidence to support it," he said.The newlyweds were staying in Truro and went on an afternoon walk near the village of Feock.
The couple had been walking along the River Fal when Mrs Prates-Schwarzacher disappeared into trees along the shore.
'Something floating'Breaking down as he gave evidence, Prof Schwarzacher said he heard a "splash" as he waited but thought it was just a boat.
Witnesses described how he arrived at the King Harry Ferry offices, a quarter of a mile from the scene, asking to use the phone "because I have lost my wife and she cannot swim".
Prof Schwarzacher told how after searching for his wife for about 25 minutes he found her face down in the river less than 100m (328ft) from where he left her.
"I saw something floating in the water close to the shore," he said, adding that he rushed into the swollen river before attempting to revive her.
"I stood in the water for a few minutes, cursing, and then walked back as quickly as I could to the ferry.
"I said to someone 'I have just found my wife, drowned' and the captain took me back in his dingy to her body."
Mrs Prates-Schwarzacher was taken by ambulance to the Royal Cornwall Hospital in Truro where she was pronounced dead.
Post mortem results showed she had died from drowning and had been suffering from gastritis that would have caused her "abdominal discomfort", the inquest heard.
A police investigation showed no evidence of foul play.
Prof Schwarzacher told the inquest he had wanted to show his Brazilian wife, who was known as Dila, places which had been important in his life.
The couple had been planning to go on honeymoon after a religious ceremony to bless their wedding the following August.
British Broadcasting Corporation
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