SEATTLE -- As a massive oil drill rig moved into Seattle, about two dozen activists in kayaks paddled to the middle of Elliott Bay, linked boats and unfurled a banner to make a stand against Royal Dutch Shell's plan to open a new frontier of fossil fuel exploration in the Arctic Ocean.

The 400-foot-long rig rising nearly 300 feet above the water dwarfed the flotilla of tiny boats on Thursday, as it passed the city's Space Needle and downtown skyline and docked at Terminal 5.

The watery protest marked a pivotal moment for an environmental movement increasingly mobilized around climate change, but the scene also suggested how outmatched Shell's opponents have been as they try to keep the petroleum giant from continuing its $6 billion effort to open new oil and gas reserves in one of the world's most dangerous maritime environments.

"The environmental issues are big and this is an opportunity to present a David versus Goliath position -- the people and the planet versus Shell -- and create a national debate about drilling in the Arctic," said Paul Adler, 52, of Shoreline, who paddled a single white kayak to "unwelcome" the Polar Pioneer.

Environmental groups in the Pacific Northwest are sensing a shift in the politics that surround energy production and have mobilized against a series of projects that would transform the region into a gateway for crude oil and coal exports to Asia.

"These proposals have woken a sleeping giant in the Northwest," said Eric de Place, policy director for Sightline Institute, a liberal Seattle think-tank . "It has unleashed this very robust opposition movement."

Added Seattle City Councilmember Mike O'Brien, who joined the so-called kayaktivists on the water Thursday: "Shell's attempt to use Seattle as a home base for Arctic drilling may be the last battle on the front of Arctic drilling, and the energy I have seen and felt from people in the region is really powerful and it gives me hope that we can stop Arctic drilling."

Shell still needs other permits from state and federal agencies, including one to actually drill offshore in the Arctic and another to dispose of wastewater. But it's moving ahead meanwhile, using the Port of Seattle to load drilling rigs and a fleet of support vessels with supplies and personnel before spending the brief Arctic summer in the Chukchi Sea, which stretches north from the Bering Strait between Alaska and Russia.

Hurricane-force winds and 50-foot seas can quickly threaten even the sturdiest ships in the seas off Alaska. But Shell cleared a major bureaucratic hurdle Monday when the federal Bureau of Ocean Energy Management, after taking public comments and reviewing voluminous reports, approved the multiyear exploration plan.

If exploratory drilling goes well, Shell plans to invest billions more in infrastructure to open this new frontier, building pipelines under the ocean and onto the tundra of Alaska's North Slope, along with roads, air strips and other facilities.

Shell's last effort to do exploratory drilling in the Arctic Ocean also left from Seattle and ended badly. The Noble Discoverer and the Kulluk -- a rig Shell had spent hundreds of millions of dollars to customize -- were stranded by equipment failures in terrible weather, and the Coast Guard barely rescued the Kulluk's crew. Federal investigations resulted in guilty pleas and fines for rig owner Noble Drilling.

The Kulluk ended up on a scrap heap in China. Shell is leasing the Polar Pioneer in its stead, again backed by the Noble Discoverer. But Shell says it has gained vital experience and can safely drill on its leases in the Chukchi Sea, as well as the Beaufort Sea, an even more remote stretch north of the Alaska National Wildlife Refuge.

Shell spokesman Curtis Smith called Monday's approval an important milestone that "signals the confidence regulators have in our plan."

Officials in Alaska have welcomed the drilling, even flying to Seattle this week to lobby for Shell's plan. Labor groups representing port workers noted that Foss Maritime is employing more than 400 people already to service the Shell fleet.

Seattle Mayor Ed Murray, for his part, is strongly against hosting Shell's fleet, warning that the port could face daily fines because it lacks the proper permit.

Those fines would amount to no more than $500 a day for the port -- a tiny drop in a very large barrel if Shell, one of the world's largest companies, manages to recover billions of gallons of oil from the Arctic Ocean.

Seattle's environmentalists, however, have a sense that their time is now.

"Unless people get out there and put themselves on the front lines and say enough is enough, then nothing will ever change," said Jordan Van Voast, 55. "I'm hopeful that people are waking up."

When the Kulluk was being prepared in 2012 for Shell's last Arctic venture, "it wasn't this big civic moment," recalled KC Golden, a senior policy adviser for Climate Solutions, an organization advocating for renewable energy.

But "now it is," Golden said. "That's a measure of how the awareness has grown. I think it's a moment for Seattle."