BANGLI, DEWATA.NEWS – A seasonal sulfur upwelling has resurfaced in Lake Batur, Bali, raising concerns among floating fish cage operators over the risk of mass fish deaths during the annual natural phenomenon.
The upwelling was observed on Monday (July 20) at several locations around the volcanic lake, including Banjar Dukuh in Abang Batudinding Village, Kintamani.
Nyoman Tilem, head of Banjar Dukuh and a local fish farmer, said signs of the phenomenon became visible around midday. Residents noticed strong sulfur odors, bluish discoloration of the lake water, and changing wind conditions, typical indicators of sulfur-rich water rising from the lakebed.
“We still don’t know how severe the impact will be on the floating fish cages. For now, fish farmers have temporarily stopped activities to reduce the risk of fish mortality,” Tilem said.
He added that no significant impact had yet been observed on wild fish, as the phenomenon had only begun a few hours earlier.
According to local residents, sulfur upwelling is a recurring natural event that typically occurs between July and August, although it can also happen at other times of the year.
Meanwhile, Wayan Agus Wirawan, Head of Fisheries at the Bangli Agriculture, Food Security and Fisheries Agency (PKP), said reports of the upwelling had also come from Kedisan and Abangsongan villages, where it began as early as 3:30 a.m. WITA.
Officials have not yet determined the severity of this year’s event.
“So far, we have not received reports of mass deaths among farmed fish. At this stage, only wild fish have been seen moving toward the shoreline,” Agus said.
He explained that if significant fish mortality occurs, it is usually visible within two to three days, depending on the extent of the sulfur spread.
The Bangli PKP Agency has deployed field officers to monitor conditions around the lake and has coordinated with a farmer in Pengotan Village who processes dead fish into organic fertilizer.
The measure is intended to prevent fish carcasses from polluting Lake Batur if large-scale fish deaths occur.
Authorities said fish farmers around the lake are generally familiar with the annual upwelling cycle, which commonly occurs between June and September and occasionally in February.
Some farmers have already harvested their fish earlier than planned as a precaution.
The fisheries agency has also reminded farmers to temporarily reduce activities around floating fish cages and immediately report any fish deaths so they can be collected and processed properly.