Radioactive contamination from Japan's Fukushima Daiichi nuclear power plant hit by a tsunami in 2011 has drifted as far north as waters off a remote Alaskan island.

Scientists said on Wednesday that analysis of seawater collected last year near St. Lawrence Island in the Bering Strait revealed a slight elevation in levels of radioactive cesium-137 attributable to the Fukushima disaster.

'This is the northern edge of the plume,' said Gay Sheffield, a Sea Grant marine advisory agent based in the Bering Sea town of Nome, Alaska.

Tsunami waves crashing over the sea walls towards Fukushima Daiichi nuclear power plant in Okuma, Japan. Traces of radioactive cesium-137 attributable to the disaster was discovered in the ocean near St Lawrence Island in the Bering Strait

The newly detected Fukushima radiation was minute. The level of cesium-137, a byproduct of nuclear fission, in seawater was just four-tenths as high as traces of the isotope naturally found in the Pacific Ocean.

Those levels are far too low to pose a health concern, an important point for people living on the Bering Sea coast who survive on food caught in the ocean, Sheffield said.

Cesium-137 levels some 3,000-times higher than those found in the Bering Sea are considered safe for human consumption under U.S. Environmental Protection Agency drinking water standards, officials said.

A 9.0-magnitude quake and tsunami in March 2011 triggered meltdowns at three of the Fukushima Daiichi plant's six reactors, spewing radiation into the air, soil and ocean and forcing 160,000 residents to flee.

The contamination from the Fukushima disaster drifted as far north as St Lawrence Island, an Alaskan island in the Bering Strait between Russia and Alaska

The Fukushima Dai-ichi Nuclear Power plant after a massive earthquake and subsequent tsunami on March 14, 2011 caused the reactors to release radioactive material into the air, soil and ocean

It was the world's worst nuclear disaster since Chernobyl 25 years earlier.

The results reported on Wednesday came from the University of Alaska Fairbanks Sea Grant program; a long-term but small-scale testing initiative.

Water was sampled for several years by Eddie Ungott, a resident of Gambell village on the northwestern tip of St. Lawrence Island. The island, though part of the state of Alaska, is physically closer to Russia than to the Alaska mainland, and residents are mostly Siberian Yupik with relatives in Russia.

Fukushima-linked radionuclides have been found as far away as Pacific waters off the U.S. West Coast, British Columbia and in the Gulf of Alaska.

Until the most recent St. Lawrence Island sample was tested by the Woods Hole Oceanographic Institution, the only other known sign of Fukushima radiation in the Bering Sea was detected in 2014 by the National Oceanic and Atmospheric Administration.

NOAA scientists found trace amounts of Fukushima-linked radionuclides in muscle tissue of fur seals on Alaska's St. Paul Island in the southern Bering Sea. There was no testing of the water there, Sheffield said.

The people of St. Lawrence Island, who live well to the north of St. Paul Island, had expected Fukushima radionuclides to arrive eventually, she said.

'They fully anticipated getting it. They didn't know when,' she said. 'The way the currents work does bring the water up from the south.'