Haragamaobama beach in Soma City, Fukushima Prefecture, was opened to the public on Saturday.
Seawalls on the beach were badly damaged by the tsunami 8 years ago. But the reconstruction work has been completed.
A ritual was held to pray for safety, and a group of local residents released balloons into the sky before the beach was officially declared open.
Children then jumped into the water all at once.
Local diners have opened beach houses to offer shaved ice with syrup on top, as well as other food and drinks.
A woman in her 30s said she is happy to once again be able to swim in the sea, where she would come every year before the disaster.
A teenage boy said he has been looking forward to the opening of the beach. He said he wants to fully enjoy himself with his friends.
Four beaches in Fukushima Prefecture have reopened since the disaster including in Iwaki and Soma.