Scientists have confirmed that radioactivity from the 2011 Fukushima nuclear disaster in Japan is detectable in the continental waters off North America, and they expect the radioactivity to peak in 2015 before gradually dissipating.

But even at its peak, the levels are expected to be far below measurements that either the U.S. or Canadian governments judge to be unsafe for drinking water or for eating fish, The Christian Science Monitor reported.

The data comes from a study published Monday in the Proceedings of the National Academy of Sciences. It says that the radiation first reached the North American Pacific continental shelf around June 2013.

On March 11, 2011, Japan's Fukushima nuclear power plant was struck by a tsunami that was set off by an offshore magnitude 9 earthquake. Three of Fukushima's four reactors partially melted because they could not be adequately cooled. In the resulting disaster, sizable amounts of radiation were released into the atmosphere and ocean waters.

Experts are particularly interested in radioactivity from cesium-137, which has a 30-year  half life. At its highest levels, the radioactivity from cesium-137 will nevertheless be well below levels that experts say are safe for drinking water.

Scientists actually track cesium-134, which loses half its radioactivity every two years, as a tracer for cesium-137.

Projections based on the latest data taken in February 2014 indicate that even when cesium-137 levels peak in late 2015, radiation is likely to remain far beneath levels that are considered a danger to people or the environment, according to John Smith, a Bedford Institute of Oceanography chemical oceanographer, the Monitor reported.

The sample of Fukushima's cesium-134 collected off the northern coast of California in August contained 2 Becquerels per cubic meter of water — less by more than 1,000 times than what the Environmental Protection Agency's limit is for drinking water, the Monitor reported.

There is still cesium-137 background radiation from nuclear-weapons tests conducted above ground in the 1950s and '60s, according to the Monitor.

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