The state land department is reminding the public that it is illegal to have ground and open fires on public beaches.

About 3 p.m. Saturday, a 4-year-old boy stepped on buried charcoal at Nanakuli “Tracks” Beach and badly burned his foot, the Department of Land and Natural Resources said.

DLNR’s Division of Conservation and Resources Enforcement has opened an investigation. It is believed someone barbecuing on the beach left the coals behind.

“Under state law, it is illegal to have fires on Hawaii’s beaches,” said William J. Aila, Jr., DLNR director-designate, in a news release. “We ask for the public’s kokua to voluntarily comply with these necessary safety requirements in order to protect our families and especially young ones.”

He said in recent years, a boy was seriously injured by hidden embers from a fire on a Maui beach and another child was burned by coals at Bellows.