More than four years after the nuclear power-plant disaster in Japan, the United Nations agency renewed pressure for an alternative to holding the tainted water in tanks and offered to help monitor for offshore radiation.

“The IAEA team believes it is necessary to find a sustainable solution to the problem of managing contaminated water,” the Vienna-based agency said in a report. “This would require considering all options, including the possible resumption of controlled discharges into the sea.’

Tepco officials are still using water to cool molten nuclear fuel from the reactors and while on-site tanks were installed to hold 800,000 cubic meters of effluent, engineers have battled leaks and groundwater contamination. The assessment, published Thursday, was based on visits by an IAEA team in February and April.

The IAEA also said it would send scientists to collect water and sediment samples off the Fukushima coastline to improve data reliability.

‘‘TEPCO is advised to perform an assessment of the potential radiological impact to the population and the environment arising from the release of water containing tritium and any other residual radionuclides to the sea in order to evaluate the radiological significance,’’ the agency said. ‘‘The IAEA team recognizes the need to also consider socioeconomic conditions .’’

Fishermen Protest
Previous releases of Fukushima contamination into the Pacific have drawn protests by Japanese fishermen and environmental groups. Fish caught off the coast of Fukushima have been subject to testing for radiation before being sold.

Contamination from Fukushima has been measured off the western coasts of the U.S. and Canada, signaling the need for more monitoring, according to the Woods Hole Oceanographic Institution, the largest private non-profit research group looking at the world’s oceans.

Though contamination levels off the North American coast are ‘‘extremely low,’’ oceans need to be monitored ‘‘after what is certainly the largest accidental release of radioactive contaminants to the oceans in history,’’ Ken Buesseler, a marine chemist at Woods Hole, said last month. - Bloomberg.