BAR, Montenegro (Reuters) - Dozens of Montenegrin environmental activists and fishermen took to the water in the Adriatic port of Bar on Monday to protest at undersea oil prospecting, which they say will endanger marine wildlife and fisheries.

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The demonstrators had already spent the previous four days walking 144 km (89 miles) along Montenegro’s coast from Herceg Novi.

“What they are doing is illegal, this is a crime against the Adriatic Sea, against nature,” said Mirsad Kurgas from the “SOS For Montenegro” watchdog.

In 2016, Montenegro awarded a 30-year offshore exploration concession for oil and gas to a consortium of Italy’s Eni and Russia’s Novatek.

The survey, which begins next week, is set to cover an area of 1,228 sq km (474 sq miles) and last 47 days. It involves a ship towing powerful air guns that cause a seismic reaction under the seabed, which can reveal the presence of oil and gas pockets.

The activists say the noise from the guns can injure or seriously disturb marine animals that rely on sound to find food, communicate and travel, potentially preventing spawning or driving them away altogether.

The Ministry of Agriculture, which approved the exploration, banned all vessels from approaching the main prospecting ship, whose arrival on Wednesday was postponed because of the protest.

ENI said it would use the advanced technology to minimize impact on the environment, and try to keep disruption of fishing to a minimum.

In a separate statement, Novatek said Montenegro’s Environmental Protection Office would be monitoring the operation and could order an immediate suspension if marine mammals or turtles were found.

The head of the National Association of Fishermen, Dragoljub Bajkovic, said Eni had offered a total of 175,000 euros ($200,000) to 127 fishermen, but that this was not enough to cover long-term disruption to Montenegro’s main fishing grounds.

“We will be suffering consequences for at least 10 years: spawning will be disrupted, fish will be annihilated,” he said.

Montenegro, a candidate for European Union membership, produces no oil, but initial data has indicated it might have enough untapped reserves to cover its oil and gas needs.

“They will probably find what they want,” said Milos Dasic, a sport fisherman, “and we shall lose what we have and love - our sea, fish and sport.”