Sri Wahyuni, Samosir, Indonesia – On retirement from public life, Wilmar Eliaser Simandjorang found a quiet place on a hillside overlooking Lake Toba, on the Indonesian island of Sumatra, to write about this landscape sacred to the region's Batak people.
"If we don't pay attention to this, Lake Toba will be just a memory," Wilmar told Mongabay Indonesia at his home near the lake, the site of a volcanic eruption 74,000 years ago that plunged the world into global winter and famine.
More recently, North Sumatra province's environment department has warned of a burgeoning pollution problem from the waste dumped into Toba, the largest volcanic lake in the world.
Many here in this subdued lakeside region today, which is home to Sumatra's ethnic Batak people (and the center of seven districts in North Sumatra province), say a complex array of changes taking place around the Toba landscape are reaching a tipping point.
"The forest is being cut down, both legally and illegally – biodiversity is being burned," Wilmar said. "Rainwater is just running off; it carries ash, trash and pesticides into the lake."
A study of 60 water samples published in the journal Advances in Oceanography and Limnology in 2024 confirms worrying local testimony. The research, conducted in 2020-2021 by scientists from the Bogor Institute of Agriculture, Indonesia's premier forestry university, indicated intensive ecological distress. Researchers revealed nitrogen levels greater than the safe threshold set by Indonesia's environment ministry, threatening both fish and water quality.
Civil society organizations, church groups and community leaders like Wilmar say land conflicts, logging and pollution of water courses have deepened the lake's troubles, even after its 2020 recognition by UNESCO, the U.N.'s culture office, as a Global Geopark of international importance requiring protection.
"This lake isn't a septic tank. This water is sacred, it's not a garbage dump," Wilmar said. "But today, just look, waste from everywhere flows straight into the lake untreated."
In his youth, working away from Toba, Wilmar often had colleagues ask him to bring them back a flask of water from the lake, such was its pristine reputation.
"Now?" he said. "Just cooking rice with it will smell."
According to Global Forest Watch, a remote sensing program published by the World Resources Institute, Samosir district saw 5,720 hectares (14,130 acres) of its old-growth rainforest cleared from 2002 to 2024. In total, Samosir's old-growth forest area has declined by about 23%.
For Wilmar, the changes taking place around the world's largest volcanic lake are a call to collective action. Consequently, he has devoted more than a decade since his retirement to fostering local environmental networks around his homeland.
"I will have to answer to God later," he said. "What have I done for my homeland?"
Planting the future
Born in 1954 in Samosir, Wilmar graduated from university on the island of Java before beginning his career as a bureaucrat. By the turn of the millennium, Wilmar led the regional development agency, Bappeda, where he worked to construct irrigation systems amid frequent droughts afflicting the uplands around the lake.
In 2004 the then-governor of North Sumatra province appointed Wilmar to run the newly established district of Samosir, pending devolved elections the following year.
Wilmar declined to run for the district office in 2005, and instead concentrated on his new focus as an environmental advocate around Lake Toba.
He began outreach work persuading local households that fruit trees could enrich both livelihoods and the landscape. Residents' groups began drawing up simple vegetation maps and implementing agroforestry designs.
"I believe forests will be sustainable if people feel they are part of their lives," Wilmar said.
He saw grassroots efforts offering advantages on the ground, where top-down government reforestation initiatives had often failed. Initially, Wilmar went about prioritizing river basins and fragile areas of the Toba landscape prone to landslide.
"At that time I wasn't planting the trees myself, but I motivated residents to understand that planting trees was like planting their own future," he said.
He said he wants primary schoolchildren to be taught to care for trees, recognize birds, water and soil.
"But if you're taught to burn weeds from childhood, that's how things will turn out,' he said.
Wider recognition for this work followed, culminating in the 2013 Wana Lestari environmental prize issued by the Indonesian government, an award he declined to accept.
"We returned it because the government didn't seem to care about our reports at the time," Wilmar said.
Lake of fire
Wilmar's rewilding efforts on the hills above Lake Toba encountered setbacks this year, amid escalating tensions around the lake.
In May this year, the leader of the Batak Protestant Christian Church (HKBP), a reformed denomination, issued a public statement calling for the largest local plantation company, PT Toba Pulp Lestari (TPL), to be shut down.
"The most painful fact is that the presence of PT TPL has triggered various social and ecological crises," the Reverend Victor Tinambunan said in a statement published on social media.
The head of Indonesia's most prominent Batak church, which claims 4.5 million followers, Victor cited air pollution, floods, landslides and gradual community breakdown over "a long journey of conflict that has never been resolved with dignity."
Juniaty Aritonang of the North Sumatra Legal Aid and People's Advocacy Association, known as Bakumsu, characterized the intervention as "spiritual leadership that supports social justice and ecological responsibility."
TPL spokesperson Salomo Sitohang responded to Victor's intervention by pointing to an environment ministry audit for 2022-2023 that found no environmental violations on the company's pulpwood concessions.
"We are open to dialogue and welcome input from all parties to create fair and responsible sustainability in the Tano Batak region," the spokesperson said in May.
In September, dozens of people from the Indigenous Lamtoras community in Sihaporas village near Lake Toba's north shore were injured in a clash with around 300 workers from TPL.
This year, wildfires scorched many of Lake Toba's hillsides, prompting Indonesia's disaster management agency to scramble specialist flights dispersing salt into the clouds in a bid to induce rainfall. The fires destroyed 16 hectares (40 acres) of land that Wilmar had worked for a decade to rewild.
"The land I turned green, which was just starting to show results, went up just like that," he said. "I reported it to the police, but there wasn't any response."
Some cases he reported to authorities resulted in criminal charges, and Wilmar's environmentalism has involved taking risks that have on occasion impacted those close to him. He recalled being chased through the forest when he encountered illegal loggers.
"They threatened me, and my son too," he said.
Now, even as age begins to slow him down, Wilmar continues to plant, to advocate, and to defend the land and lake he calls a blessing.
"We can turn this destruction into hope," Wilmar said. "But it takes will, knowledge, and love."
[Additional reporting by Ayat S. Karokaro and Richaldo Hariandja.]
Citation
Hastuti, Y. P., Nirmala, K., Hutagaol, M. P., Tanjung, D., Kriswantriyono, A., Nurussalam, W.,... Fatma, Y. S. (2024). Analysis of main components of Lake Toba's water quality in different seasons. Advances in Oceanography and Limnology, 15(1). doi:10.4081/aiol.2024.11726