Spanish police say several people may have been thrown overboard during the attempted sea crossing from Mauritania.
ADVERTISEMENTAt least 25 migrants are feared to have died at sea during an attempted sea crossing near Spain's Canary Islands.
Spanish police said that several migrants were "thrown overboard" based on survivors' testimonies.
Forty-eight people on the boat survived and arrived on Sunday on the Spanish island of El Hierro, police added.
The migrant vessel is believed to have left Nouakchott in Mauritania before attempting to cross the Atlantic Ocean.
About 75 people -- including some children -- had left Mauritania on 19 March, Spanish police said on Thursday.
"In a few days the water supply ran out and they had only biscuits to eat, which would have forced those hospitalised survivors to drink salt water to quench their thirst."
Authorities also said that the boat's captain had imposed "harsh conditions" during the attempted crossing and had even tied up and beaten one man.
Three of the migrants who arrived on the island are suspected to have been in charge of the vessel and have been arrested.
Spain remains one of the main entry points for illegal migrants trying to reach European soil.
A total of 5,552 migrants have arrived in the Canary Islands between 1 January and 15 March this year, according to Spain's Interior Ministry. The number represents more than double the figure in the same period last year.
In 2021, more than 40,000 migrants -- mostly from Morocco -- arrived by sea on Spanish land.
Meanwhile, at least 1,255 people died during migrant crossings attempts last year -- the highest since the United Nations International Organisation for Migration (IOM) began compiling records in 2014.
But Spanish NGOs estimate that the number of fatalities in 2021 was as high as 4,404.