Slovenia preventively shut down production Sunday at its only nuclear power plant after a steep increase in the flow of the Sava river used for cooling the system, the Krsko nuclear plant said in a statement.

The plant's production was stopped manually due to the "great amount of leaves and other garbage on the Sava river that had decreased the efficiency of the cooling system on the secondary side of the plant," it said.

"During the shutdown, all the systems and equipment worked as expected. There were no undesired effects on the environment and people," the statement added, saying production would resume over the following days after the event is analysed and the system checked.

Strong rain and snow over the weekend caused a steep increase in the level and flow of all rivers in Slovenia, including the Sava river, which flooded its banks and ran into adjoining lands in many regions.

The Krsko nuclear plant was shut down last April for a regular 42-day maintenance after its 25th fuel cycle, during which it produced 8.5 terawatt hours (TWh) of electricity.

In February, the Krsko plant, 90 kilometres (55 miles) east of the capital Ljubljana, briefly reduced output to one-third following a small oil leak.

Before that in March 2011 it had temporarily halted operation when a loss of coolant in the reactor's cooling system forced an automatic shut down.

The plant -- jointly built with Croatia in 1984 when they were both part of the former Yugoslavia -- accounts for about 40 percent of the EU country's electricity production.