Twenty-one people, most of them women, were killed last night when a traditional flat-bottomed boat overturned off Bettenty, a central Senegal island area, with 72 on board, said Commander Oumar Kane, a senior Senegalese firefighting official.
All except two present were women, and another 51 people had been rescued, he added.
Bettenty lies in the Saloum delta where such boats, known as pirogues, are often used for travelling between the mangroves and from one islet to another.
The second incident took place last night in the River Gambia, the waterway which splices tiny Gambia almost into two, said police spokesman Foday Conta in Banjul.
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"Eight fishermen died yesterday night after their boat capsized," he told AFP.
"Their boat capsized in the river between the villages of Diabugu and Tabajang in the Upper River Region of the country. They were on board a fishing canoe," Conta added.
Reporting on the incident in Senegal, L'Observateur daily said the boat had capsized in high winds, while other newspapers said it had foundered because it was overloaded. Senegalese radio station RFM said some of the women were pregnant.
Meanwhile Senegal's official APS news agency reported that Fisheries Minister Oumar Gueye was en route to the site of the tragedy to present the government's condolences.
Several Senegalese papers recalled the Joola tragedy of 2002 when a ferry sank during a storm, killing more than 1,800 people in what was one of the world's worst-ever maritime disasters.
Only 64 people were rescued.
Boat accidents in both nations are often deadly as fishermen and ordinary citizens use canoes or makeshift boats to travel but often lack lifejackets, while many cannot swim.