More than 4,400 migrants died last year attempting to reach Spain by sea, the Spanish NGO Caminando Fronteras announced on Monday.
There have never been as many fatalities on the route as there were in 2021.
The number is almost double the figure recorded in 2020, when 2,170 migrants are believed to have died on the route.
Some 4,016 people died attempting while attempting to travel from West Africa to the Canary Islands alone, the organization said.
The Caminando Fronteras figure is three and a half times larger than that recorded by the UN Organization for Migration (IOM). The Spanish organization says its activists have close contact with survivors of accidents and migrants' families in Africa.
In all cases, it said, data from primary sources is cross-checked with information from migrant communities, official bodies and NGOs working in the field.
The IOM website adds a disclaimer that: "As fatal accidents are often registered weeks or months later, the final death toll in 2021 is likely to be much higher."
Caminando Fronteras said that that the 4,404 total victims include 4,175 confirmed deaths as well as 229 migrants who disappeared months after the start of a migration attempt and are almost certainly dead. Among the victims were 628 women and 205 children.