The incident occurred in the municipality of Nidau, Bern cantonal police said.
Police believe from the initial findings that the man was trying to retrieve a ball that had fallen into the water.
The accident occurred in a canalized part of the river, known as the Nidau-Büren Canal, just before it connects with Lake Biel.
Officers were contacted about the drowning at 1.50pm.
When police arrived at the scene the man was nowhere to be seen.
Almost two hours later, police divers retrieved his body in water six metres deep.
Police have ruled out foul play in the matter.
It may seem like an early start to the swimming season, but temperatures hit 25 degrees or more in many parts of Switzerland on Wednesday.
The mercury rose to as high as 27.8 degrees in Sion in the canton of Valais, according to SRF Meteo, the weather service of the German-language national broadcaster.
Temperatures are forecast to remain well above 20 degrees on Thursday as a warm spell begun on the weekend continues, following a cooler than usual start to spring.
The summery conditions are expected to be short-lived however, with a cold front predicted to arrive on Friday, followed by snow at levels above 800 metres.