(AP) – The parents of a 12-year-old boy who was swept into the Pacific Ocean in January said they didn’t know the hidden danger of sneaker waves that sometimes strike Northern California beaches.

Arunay Pruthi was dragged underneath a huge wave on Jan. 18 during a family outing to Cowell Ranch State Beach, a secluded cove about 30 miles south of San Francisco. The wave hit him as his parents struggled to save his 8-year-old brother from another powerful wave that crashed over the younger boy.

Despite an exhaustive search along the coastline by authorities and a privately organized one by his family, Arunay’s body has not been found.

He was among 12 people who were fatally swept from Bay Area beaches into the sea from November to January, a period that was far deadlier than any stretch authorities had seen before, the San Francisco Chronicle reported Saturday.

The victims included a 4-year-old girl who died after being dragged into the surf on a Thanksgiving Day outing to McClures Beach at Point Reyes National Seashore, a 40-year-old father who drowned while trying to save his two children who had been swept from Blind Beach in Jenner to sea on Jan. 3, and a wave that overtook a 37-year-old woman as she and her husband looked for sea urchins at Pescadero State Beach on the San Mateo County coast.

Some of the deaths occurred on days authorities had issued warnings about dangerous high tides, rip currents and sneaker waves. Sometimes called sleeper waves, they form during offshore storms that transfer energy to the ocean surface. The waves typically arrive during periods of calm and travel far higher up the shore, catching victims by surprise and dragging them into the ocean as the ground beneath their feet “suddenly becomes inundated,” researchers at Oregon State University wrote in a 2018 paper.

Arunay’s parents said they hadn’t heard of the phenomenon when they went to the beach to meet with a group of friends. There is only a small blue sign near the stairs leading down to the beach that reads, “Tsunami hazard zone,” nothing against sneaker waves.

Sharmistha and Tarun Pruthi said they want to create a foundation in their son’s name to advocate for beach safety.

Several public officials said they believe Bay Area schools should teach children how to avoid sneaker waves and rip currents.

“Never tell a parent, ‘These things happen,’ ” Tarun Pruthi said.