According to The Guardian's Lorenzo Tondo, Gasol dove into the water to help a woman clinging to a piece of wood. Two dead bodies, including that of a toddler, were rescued alongside her.
"There was that woman, with her elbows resting on a wooden beam," Gasol said. "Her eyes were lost in the void. She was weak and in shock. She had been clinging to that piece of wood with her last bit of strength and had remained that way for 48 hours. I thought of this woman, of her strength. And I felt anger."
Gasol said he is haunted by the image of the drowned child.
"I will never forget that child," he said. "I am a father. I have children. And I imagine the pain of a father who is forced to face a journey like this where one risks everything, one risks one's own life, to reach a country where one can live in peace and with dignity."
The 33-year-old Gasol and his older brother Pau have been volunteering with charity Proactiva Open Arms, which is trying to assist with the mass of migrants crossing the sea. According to the United Nations, 1,443 people have died or have gone missing while attempting to cross the Mediterranean so far this year.
Gasol had initially chosen not to publicize the activity, but outrage from the incident where the woman was rescued caused him to tweet about it on Tuesday.
"It was too important not to tell the world," he said. "I could no longer remain silent."