PORTLAND, Ore. (KRON/AP) — Activists rappelled off a bridge in Portland Wednesday as part of an effort to block a ship to be used by Shell for Arctic oil exploration.

Demonstrators dangled from the St. Johns Bridge while so-called “kayaktivists” held their protest on the Willamette River, which runs through downtown Portland.

They’re trying to block Wednesday’s scheduled launch of an icebreaker ship, the Royal Dutch Shell PLC Fennica. The vessel arrived in Portland for repairs last week. It was damaged earlier this month in the Aleutian Islands when it struck an underwater obstruction, tearing a gash in its hull.

The icebreaker is a vital part of Shell’s exploration and spill-response plan off Alaska’s northwest coast. It protects Shell’s fleet from ice and carries equipment that can stop gushing oil.

Opponents of Arctic drilling worry that the area’s remoteness and rough conditions will hamper cleanup efforts in the event of a spill. They also say Arctic drilling threatens the pristine wilderness of one of the most environmentally sensitive regions in the world.

Shell has maintained that it has a comprehensive safety and cleanup plan in place should a spill occur.

Greenpeace USA executive director Annie Leonard said the activists have enough water and food to last for days, and can hoist themselves to allow other marine traffic to pass.