Oulu hydro plant failure sent ice masses into central park, regulators say

The Merikoski hydroelectric plant in central Oulu shut down three times in a single day in mid-February 2026 after rime ice on power lines caused them to sway, triggering turbine protections, according to an investigation by Finnish public broadcaster Yle and regulatory authorities.

The repeated stoppages forced emergency spillway releases of up to six million cubic meters of water, pushing large ice masses from the Oulu River into the nearby Ainolanpuisto park. The ice blocks made movement in the park hazardous.

Finland’s Permit and Supervisory Authority (LVV) stated in a recent opinion that the risk of a dangerous situation was obvious during the incident. The Lapland Centre for Economic Development, Transport and the Environment (ELY Centre) also investigated. Timo Regina, a dam safety expert at the ELY Centre, said the case was highly unusual in Finland and that he could not recall a similar event.

The plant operator Oulu Energy said the power line disturbances, caused by rime ice falling and swinging the lines, shut down all turbines simultaneously three times over 15 hours. As a result, water levels rose rapidly, forcing the operator to open spillway gates. According to LVV, the gates opened slowly and ice accumulation beneath the water surface hampered their operation. Water levels exceeded the permitted upper limit three times and also fell below the lower limit.

In total, the plant discharged about six million cubic meters of water in just a few hours.

Grid operator Fingrid also examined the case. LVV has demanded that Oulu Energy ensure the spillway gates function more reliably in the future. No sanctions were imposed.

Oulu Energy declined to provide detailed answers about the sequence of events, the causes, or the performance of safety systems. The company initially struggled to confirm whether the plant meets the required eight-hour backup power capability. It later stated that the required backup capacity is in place and that critical systems functioned as designed.

A similar incident occurred at the Merikoski plant in 2021, when a transformer failure caused more severe water level rises and also revealed problems with the spillway gates. Oulu Energy said it improved gate heating and maintenance after that event. Regulators noted that the risk of such weather phenomena is expected to increase in the future.