A large mass of dead fish was first spotted floating in the Bay of Biscay off La Rochelle on Thursday. The public was alerted of the occurrence by the French branch of the environmentalist group Sea Shepherd.

The spill consisted of “more than 100,000” dead fish, measuring about 3,000 square meters (32,300 sq ft), according to the group’s estimates. The group said the Bay of Biscay has been a hot spot for industrial fishing involving multiple vessels with onboard processing plants. Among others, they include the world’s second-largest Lithuania-flagged trawler FV Margiris active in the area.

Sea Shepherd France alleged the fish were “thrown overboard” by one of the trawlers, condemning industrial fishing as “pillage.”

French Maritime Minister Annick Girardin had a similar reaction, describing the imagery of the dead fish as “shocking.” The official said she had launched a probe to identify the causes behind “the significant discards of fish.”

The nature of the spill, however, did not remain a mystery for long. On Friday, fishing industry group the Pelagic Freezer-Trawler Association (PFA), representing the owners of the vessel, said the spill was accidental, officially naming FV Margiris as the culprit.

“An amount of blue whiting was involuntarily released into the sea from the Margiris vessel due to a rupture in the cod-end part of its net,” the statement reads. “Such an accident is a rare occurrence and in this case was caused by the unexpectedly large size of the fish caught.”

The PFA group pointed out blue whiting is a quota species of fish, with the lost fish to “be deducted from the vessel’s quota.” “It is not in our members’ interest to lose any fish they take on board and we regret that this fish will now not be available for human consumption,” it added, rejecting the allegations the spill was somehow intentional.