Sun Moon Lake: What Lies Beneath 18.18 Meters of Water — Taiwan's Drowned Heart

30-second overview:
Sun Moon Lake has two identities: Taiwan's most visited tourist lake, and the country's largest grid-scale pumped-storage battery. In 1934, Japanese hydroelectric engineering raised the water level by 18.18 meters, permanently inundating the Thao people's ancestral villages and farmland — but also inaugurating a century of hydropower history in Taiwan. Today it anchors the island's largest pumped-storage system, with lake water cycling through 380 meters of elevation between night and day, providing the most reliable backup power to this island.

In June 1934, with the completion of the Sun Moon Lake No. 1 Power Station (now Daguan Power Plant I), water from the Zhuoshui River was channeled into this once-quiet natural lake. The water level began its slow, steady climb — ultimately rising 18.18 meters above the original lake surface. Those 18.18 meters were a geographic and cultural upheaval: a lake originally about 5.75 square kilometers in natural area with a maximum depth of only about 4.8 meters expanded to roughly 7.73 to 8.4 square kilometers at full level, reaching a maximum depth of 27 meters, with its water storage capacity increasing approximately 6.72-fold. The farmland and villages where the Thao people had lived for generations — including the settlement known as "Shih Yin Old Village" (石印舊社) or the Water Village (水社部落) — sank beneath the water forever.¹²¹²

The Floating Fields That Vanished — and the People Who Were Moved

For most visitors, Sun Moon Lake's "beauty" comes from the expanse of blue water. For the Thao people (邵族), it was a forced farewell. Before the water level rose, the Thao cultivated what they called "floating fields" (浮田) — agricultural plots built by piling grass and mud on the lake's surface. These fields ranged from thousands of square meters down to a single square meter, anchored in place or drifting with the wind. The Qing Dynasty scholar Lan Ding-yuan wrote in Account of the Shuishalian Region (《紀水沙連》): "All around is water. The local people grow crops on fields of grass floating on the surface, drifting about with the wind."³¹³

Yet to supply Taiwan's electricity needs, this drifting paradise was sacrificed. The rising water submerged the Thao's old villages and floating fields, forcing a people once sustained by farming and fishing to pivot toward performing for tourists and making crafts.⁴ In recent droughts — 2021, for instance, when water levels fell to around 738 meters elevation — the submerged Water Village ruins surfaced after nearly a century underwater: stone walls, artifacts, and even a Qing-era tombstone from some 178 years ago, along with large Thao dugout canoes — mute witnesses to the drowned memory and the wider extent of the ancestral settlement.⁵¹⁴

📝 Curator's Note:
When we stand on the shore admiring the light on the water, what lies beneath our feet is another people's loss. The "beauty" of Sun Moon Lake is, at its core, an engineering miracle built on sacrifice.

Taiwan's Largest "Pumped-Storage Battery"

If you visit Sun Moon Lake late at night, you may notice the water quietly rising — the island's largest pumped-storage system is running, pumping water from the downstream reservoir back up into the lake for storage. Sun Moon Lake and the downstream Mingtan and Minghu reservoirs together form an enormous energy cycle.

The Sun Moon Lake hydropower project (begun 1919, completed 1934) was a major milestone in Taiwan's modernization. The project diverted water from the Wuji Dam on the upper Zhuoshui River through an approximately 15-kilometer underground tunnel bored through Shuishe Mountain into Sun Moon Lake; the water discharged after generation flows into the Shuli River. To transport construction materials, the Jiji Branch Railway (集集線) was born as a direct consequence.¹⁵ The Shuishe Dam (30.3 meters high) and Toushe Dam (10.08 meters high) are the primary structures that raised the water level. An overflow shaft along the lake shore near the Shuishe Dam — resembling an "eagle-eye skylight" — serves as a critical safety mechanism, draining excess water when levels run too high to prevent dam overflow.¹⁶

During off-peak nighttime hours, the system uses surplus power to pump water from the lower reservoir back up into Sun Moon Lake (the upper reservoir); during daytime peak-demand periods, water is released to generate power again. The Mingtan Power Plant's installed capacity reaches 1,602 MW — exceeding even the capacity of Nuclear Power Plant No. 1.⁶ This up-and-down cycling causes the lake level to fluctuate by nearly 2 meters each day. The famous "Nine Frogs Stacking" sculpture, originally designed to promote ecological awareness, has become the island's most intuitive indicator of water shortages and the lake's power-generation pulse.⁷

Worth noting: in 1944, Daguan Power Plant I was damaged by U.S. bombing and generation halted temporarily. In recent years, Taipower has pushed a "Pumped-Storage 2.0" upgrade plan — raising the downstream Minghu Reservoir dam by 1.9 meters, adding nearly 1 million tons of storage capacity (to a full-capacity 7.9 million tons), and projecting 222.3 million additional kWh generated annually, further reinforcing Sun Moon Lake's role as "Taiwan's largest battery." Daguan Plant II and Mingtan Plant combined have approximately 2.6 GW of installed capacity; Mingtan alone delivers 1,602 MW, generating about 2.4 billion kWh annually. Pumped-storage operations cause the water level in the lower reservoir (Minghu) to fluctuate up to about 28 meters daily, creating a localized "tidal" landscape.¹⁷¹⁸

Thao Culture and Ancestral Grounds: The Changing History of Lalu Island

Sun Moon Lake is the ancestral home of the Thao people; their culture and legends are inseparable from the lake. The most celebrated is the "White Deer Legend": Thao ancestors originally lived near the Chianan Plain or around Alishan. While hunting, they chased a white deer across the Central Mountain Range and eventually arrived at a place called "Puzi" (土亭仔). The white deer leaped into the lake; the hunters discovered the land was rich in fish and shellfish, the soil fertile, and they settled there.¹⁹

Lalu Island (拉魯島, formerly called "Pearl Islet" or "Guanghua Island") holds supreme importance in Thao culture as their highest ancestral spiritual ground; the Indian coral tree on the island symbolizes the male ancestral spirit. Its history is one of constant change: at various times it was home to both Thao and Han Chinese; in 1879 a plague scattered the population (others attribute this to a Han Chinese hexagonal pavilion disrupting feng shui). Under Japanese rule, a Gyokushima Shrine was built on the island. After the water level rose, the island shrank. The 921 earthquake partially submerged it. The Thao people actively fought to reclaim control of their ancestral spiritual ground, ultimately restoring its name to "Lalu," relocating the "Old Man Under the Moon" deity statue from the original Lalu Island to the lakeside Longfeng Temple, and imposing a complete ban on general visitors landing on the island — as a mark of respect for the ancestral spirits.²⁰²¹

Thao culture has many distinctive features: the ancestral spirit basket (holding the clothing and ornaments of ancestors) must be venerated at all life-cycle ceremonies. Under Japanese rule, the "pestle music" performance became a tourist highlight but also brought the pressure of commercialization. In recent droughts, the "Swing Festival" (鞦韆祭, a traditional Thao ceremony) was re-enacted near the lake's receding shoreline, reconstructed on newly exposed ground to recreate the old lakeside image — as documented by anthropologists in 1958. It is worth noting that Japanese colonial-era scholarship once suggested the Thao were a sub-group of the Tsou people, but differences in language and ritual are significant; the Thao were officially recognized as Taiwan's 10th indigenous people only in 2001.²²²³

Water Levels and the Nine Frogs: The Natural Pulse and the Human-Made Gauge

The Nine Frogs Stacking sculpture sits along the Shuiwa Head Trail (between Dazhu Lake and Ita Thao); each frog's head marks a different elevation, with the lowest frog at 745.90 meters. When all nine frogs are exposed, it does not necessarily mean severe drought — at that level, storage rates are still around 60%; the exposure mainly reflects the 1-to-2-meter daily fluctuation from pumped-storage operations and seasonal water conditions. In recent years, all nine frogs have been exposed multiple times — in 2015, 2020, 2021, 2023, and 2026 — with exposed mud at the base. By late March 2026, due to limited spring rains and heavy generation demand, water levels dropped to approximately 741.6 to 742 meters (more than 6 meters below full capacity), giving Taipower the opportunity to conduct dredging and cleaning.⁷²⁴

Mass Swimming and Tourism's Environmental Tug-of-War

Once a year, around the Lunar July or August period, Sun Moon Lake sees its most boisterous moment — the mass open-water swimming event. First held in 1983 with only 557 participants, it has evolved into an international event drawing tens of thousands annually. In 1995, the International Olympic Committee recognized it as the largest open-water swimming event in the world.⁸⁹ The 43rd edition in 2025 had 24,736 registered participants (including 361 international swimmers from 35 countries and 130 swimmers with disabilities), setting a recent high. The 2026 edition is planned for September with registration capped at approximately 20,000.²⁵

Yet the event brings environmental challenges. Local businesses welcome the crowds, but environmental groups and some residents worry about the burden that tens of thousands of people in the water within a short time places on water quality.¹⁰ This tug-of-war between "tourism value" and "ecological sustainability" mirrors the pressures Sun Moon Lake faces today. Additionally, land consolidation in 1983 has led to fragmentation of Thao land; commercial development (hotels, BOT concessions) has conflicted with ancestral worship, and some development environmental impact assessments have been criticized for failing to adequately assess impacts on Thao culture (such as interference with ritual practices).²⁶

Coda: Between Sun and Moon

"To the mountain's south the water is round like the sun; to the mountain's north the water bends like a half-moon." The Qing-era writer Cao Shi-gui defined the lake's name in Diary of an Official (《宦海日記》) this way.¹¹ Sun Moon Lake was historically known by names including "Shuishalian Lake," "Shuishe Lake," and "Dragon Lake." The Wenming Temple features a "Year Staircase Walk" (366 steps, one per year of life, inscribed with solar terms and notable names) — a symbol of the blessing of years.²⁷

Sun Moon Lake today still shifts its colors between sunrise and sunset, but the deep mountain water's world of isolation sank into history in 1934. It is the artery of energy, the scar of ethnic displacement, the showcase of tourism — and it must constantly navigate among energy demand, ecological sustainability, and Thao tradition. The next time we stand at the Shuishe Pier watching Lalu Island emerge from morning mist, we might try listening to what lies beneath 18.18 meters of water — the whisper of Thao ancestral spirits, and the unceasing electrical heartbeat of this island. In drought years, when ruins or rituals resurface, they remind us that beneath the lake bottom there are still submerged villages and drowned memory.

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