Eleven people are confirmed dead and five others remain missing after a boat sank on Lake Titicaca, Bolivian authorities said Wednesday.

The vessel went down about 1 mile from Suriqui island due to excess weight, regional naval commander Pablo Cardona told the media.

At least 20 people were aboard the boat, most of them teachers returning to the mainland after taking part in a school event on Suriqui.

The fatalities include three minors, one of them a 5-year-old girl. Another child is among the five people unaccounted for.

Four other passengers managed to cling to the capsized boat until rescuers arrived, Cardona said.

Lake Titicaca, the world’s highest navigable body of water, is shared by Bolivia and Peru.