Norway’s police security service (PST) said it suspects that pro-Russian hackers sabotaged a dam in the country’s southwest in April — the first time state officials have publicly linked the incident to Russia.

PST chief Beate Gangas disclosed details of the case on Wednesday, according to local newspaper VG, warning Norwegians to prepare for more Russia-linked cyberattacks. She said such operations aim to sow fear and unrest in Norway and undermine its security.

Local media previously reported that the hackers breached the dam’s control system, opening valves for four hours and sending large amounts of water gushing into the Riselva River until operators regained control. 

The small dam is used for fishery purposes and not part of the power grid, but released about 500 litres (132 gallons) of water per second before the breach was detected and stopped. Officials said the attack was unsophisticated but carried symbolic weight, given Norway’s reliance on hydropower.

No group has been formally blamed, but a pro-Russian collective calling itself Z-Alliance claimed responsibility in April. The group has previously boasted of intrusions into industrial control systems in multiple countries.

In February, Norway’s intelligence services warned that Russia would continue subversive activities against the country, likely targeting logistics and energy infrastructure.

Russia-linked hackers have been linked to previous water-related incidents abroad. In April 2024, a Russian group claimed a cyberattack on a water and wastewater treatment plant in Indiana, and it was also suspected in a January attack that caused a tank overflow at a water facility in Muleshoe, Texas.

The Russian embassy in Oslo rejected the allegations, accusing Norway of making politically motivated claims without evidence. In a statement, it said such accusations were part of a broader “hybrid war” waged by Norway and its Western allies against Russia, alongside arms supplies to Ukraine and sanctions.

The embassy said Moscow had repeatedly offered to cooperate on cybersecurity with Norway, but received no response. It warned that Norway’s actions made it “a dangerous country” for Russia and a threat to its national security.