A spokesperson for the States of Alderney said it happened during “a period of strong north-easterly winds combined with the big spring tide”.
Above: States of Alderney Member Alex Snowdon filmed the pontoon sinking in the harbour this morning.
Harbour Master Adam Rose said structural damage to the pontoon’s couplings caused one section to take on water.
“We will aim to disconnect the outer sections and crane them out of the water as soon as is practicable,” he said.
“In the meantime, the passenger landing pontoon that was introduced last year will be able to accommodate the amount of traffic expected between now and the end of the season.”
The pontoon was due to be removed in stages throughout September and October as harbour services are reduced after a busy summer.