T

he government’s attempts to turn Lake Toba, the largest permanent body of water in Southeast Asia, into a first-rate tourist destination is facing a major hurdle, as a recent study found that pollution in the lake led to the deaths of millions of fish last month.

The study, conducted by the Environment and Forestry Ministry following the sudden death of millions of fish, revealed that the amount of phosphorus in the lake was 300 percent greater than it was in 2012.

Phosphorus is a common constituent of agricultural fertilizers, manure and organic waste in sewage and industrial effluent. It is an essential element for plant life, but when there is too much of it in water, it can speed up eutrophication (a reduction in dissolved oxygen in water bodies caused by an increase of mineral and organic nutrients) in rivers and lakes.

The mass death of fish in Lake Toba was down to an oxygen shortage, and led to losses of billions of rupiah. The oxygen shortage is believed to be caused by the alarmingly high amount of phosphorus in the water.

The ministry’s pollution director-general, Karliansyah, said that the toxic amount of phosphorus was caused by mismanagement of the lake.

“We have some recommendations. First, the sources of pollutants must be cut by 43 percent or 212,295 kilograms per year,” he said.

The pollutants originate from hotels, residences and agriculture, Karliansyah explained. “Detergents from households and hotels contribute the most. That’s why we’re asking domestic wastewater treatment plants owned by regional tap water companies to be optimized,” he said.

Besides that, the expansion of fish breeding in the lake has also worsened the water quality. The lake is home to 12,000 keramba (floating net cages) owned by local residents and entrepreneurs, but the local administration suggests that the number should be cut to a third of that.

Some cages, moreover, are overcrowded, containing 10,000 fish, despite their capacities being 3,000 — 5,000. The concomitant excessive use of fish fodder has increased the level of phosphorus in the water.

“We recommend that the number of fish in keramba be decreased by 44 percent,” said Karliansyah.

PT Aquafarm Nusantara, one of the biggest keramba fishery companies in Lake Toba, acknowledged the food pellets it had scattered in its keramba in Lake Toba had caused a decrease in water quality, but denied they had had a severe impact.

Long before last month’s fish deaths, the local Batak community had complained about environmental destruction and water pollution in Lake Toba, but the government has yet to outline any concrete actions to halt the damage.

Instead, it plans to promote tourism around Lake Toba, on Samosir island and in seven regencies that share the lake. Direct flights now operate between Soekarno-Hatta International Airport and Silangit Airport. A toll road is also to be built to shorten the travel time to reach the lake overland.

The government recently established the Lake Toba Authority to oversee licenses for the 500-hectare tourism area.

The environment ministry’s river and protected forest director-general, Hilman Nugroho, meanwhile said that the government was well aware of the problem, estimating that 16 percent of the lake was in critical condition.