KOBE (Kyodo) -- Hyogo Prefecture, which is suffering from poor catches of some fish, has decided to allow greater discharges of nitrogen and phosphorus into a nearby sea in western Japan, deeming the water has become too clean for fish to live in, officials said Monday.
The prefecture plans to set what it sees as Japan's first lower limit on the substances affecting the marine environment, possibly within this year. The nonbinding standard includes keeping the minimum nitrogen amount at 0.2 milligrams per liter of sea water in the Seto Inland Sea.
The prefecture also plans to ask local municipalities and companies to cooperate with its plan to relax standards on domestic and industrial wastewater discharges.
"We want to release waste water carefully by consulting research organizations and experts so that we don't drastically change the marine environment," said an official at the prefectural government.
The Seto Inland Sea frequently experienced red tides during Japan's high economic growth period from the mid-1950s to the early 1970s as factory waste water with abundant nitrogen and phosphorus flowed into the sea, causing abrupt increases in the plankton population.
Japan has since toughened environmental controls and introduced better waste processing technologies. The central government has set the upper limit of nitrogen in the sea at 0.3 mg per liter for the prefecture, and the actual amount stood at 0.17 mg in fiscal 2016.
But as the amount of the substances declined, so did the plankton that fish feed on. Hyogo prefectural officials say the lack of plankton has led to the recent poor catches of sand eel, a popular spring delicacy in the region.
This year's sand eel fishing period in March was terminated after three days in the prefecture due to serious poor catches. The period used to go into May.
Prefectures and municipalities located along the Seto Inland Sea have also been working to increase the amount of such substances in seawater.
The city of Fukuyama, known for its seaweed farming, released water with higher levels of nitrogen during the winter on a trial basis in 2015, while Tokushima Prefecture has taken similar measures since 2016.