Anyone looking for the most under-reported story of the spring in California need seek no further than the tall stalks of kelp swaying back and forth just beneath the ocean surface along much of the California coast.

Fish eat kelp; so do small crustaceans near the bottom of the food chain that themselves are later consumed by larger fish that sometimes become food for humans. The largely-neglected news story is that it’s been somewhat radioactive off-and-on for months and it concentrates Iodine 131 isotopes at levels 10,000 times higher than what’s in the surrounding water.

At the same time, steam generator problems have kept the San Onofre nuclear generating station near the Orange-San Diego county line closed for three months, with no reopening in sight as California heads into the summer season of peak electricity consumption. This combination of events ought to have California authorities deeply questioning the state’s heavy reliance on power from both San Onofre and the Diablo Canyon atomic plant on the Central Coast.

The facilities aren’t due for relicensing until the early 2020s, but the utilities that own and operate them began preparing last year for license renewal proceedings.

Despite absorbing radioactive iodine isotopes, the California kelp is still not “hot” enough to endanger diners — at least so far as is now known. But lobsters and some species of fish like mullet concentrate and retain radioactivity, which would increase with any newly “hot” seawater.

Just 15 months ago, none of this was a worry. San Onofre was running smoothly. The kelp was fine. Things were even copacetic at Diablo Canyon, where skeptical state legislators wondered whether an earthquake fault discovered after the plant was built might produce temblors larger than the 7.5 level it was made to withstand.

But then came a great Japanese earthquake and tsunami last year, followed by meltdown and significant leakage of radioactivity from that country’s Fukushima Daiichi generating station.

Contaminated iodine and cesium rose into clouds that crossed the Pacific and dumped heavy rain along the California coast about one month later. Shortly thereafter, two scientists from Cal State Long Beach tested kelp from various parts of the Pacific Coast, finding no radioactivity off Alaska, but plenty of iodine and cesium isotopes off California.

The fallout from the Japanese disaster was sufficient to force evacuation of large swaths of that nation’s east coast. And while Iodine 131 has a half life of about a month — meaning it wasn’t a threat for long unless fish or crustaceans concentrated it much more heavily than was found in the kelp they ate — the cesium (detected only in lower concentrations so far) lasts much longer, and will likely remain in sea life for more than 30 years.

At the same time, the problems at San Onofre — operated by Southern California Edison Co. — remain unexplained. The federal Nuclear Regulatory Commission says it won’t allow a restart until the pattern of premature wear in steam generator tubes is explained and corrected. The agency is normally the nuclear industry’s best friend and enabler in government.

Off Diablo Canyon, Pacific Gas & Electric Co. is spending $64 million to make the first precise map of seismic faults offshore from that generating station. But even that survey probably will not produce full answers to questions about how much danger may exist, because PG&E will measure neither the pace of possible tectonic plate slippage nor the frequency of past quakes in the immediate area. Instead, the utility says it will depend on calculations of assumed slip rates.

That kind of incomplete data might have been one enabling factor in the Fukushima Daiichi disaster, which demonstrated that even a partial meltdown many thousands of miles away can produce measurable radiation increases here.

No one knows how much more contamination a Fukushima-like quake and tsunami near either San Onofre or Diablo Canyon could cause. Nor does anyone yet know how bad the problems may be at San Onofre.

If these questions don’t reinforce the need for meticulous analysis in considering relicensing the two California nuclear stations, it’s hard to see what could.

For sure, no one looks more prescient today than the 10 legislators who wrote the NRC weeks before Fukushima begging for public hearings in California before the renewal proceedings go very far. The point was not necessarily to deny renewals, but to take them slowly and with a maximum of public information.

What happened afterward in Japan and at San Onofre makes hearings all the more imperative, while also highlighting the need for very careful analysis of all potential hazards and the reliability of all safety and mitigation measures.

Thomas D. Elias is a writer living in Southern California and author of “The Burzynski Breakthrough.” Write to him by email at tdelias@aol.com.