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Sihwa Tidal Power Observatory: A Dead Lake's Second Act

Visited in person

Last verified: 2026-09-03. Rules and prices change — always confirm on the official site before you travel.

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There is no collection here, no glass case, no wall of artifacts. The Sihwa Tidal Power Moon Observatory is a 75-meter tower standing on top of a working power plant, and the building is the whole exhibit — you are climbing a machine that is still running underneath you.

The 75-meter Sihwa Narae Moon Observatory tower rising from the tidal power plant on Daebudo, seen from the park below with an Ansan sign in the foreground
The observatory tower rising from Daebudo, its glass dome catching the light above the tidal plant it stands on. Photo: Colors Korea, Site visit · © Colors Korea

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The lake the tidal plant was built to fix

Sihwa Lake died within a few years of being sealed off. Engineers finished the seawall closing it from the sea in 1994. The water rotted almost immediately. Chemical oxygen demand, the standard pollution measure, jumped from 2–3 ppm before the wall to about 17 ppm by 1997, as industry and unfinished sewage systems drained straight into a lake with no outlet. Korean reporting from the period called it, literally, the “Lake of Death.”

The fix, in the end, was to let the sea back in. Engineers reopened the sluice gates for seawater exchange from 1997 to 1999, and officials formally reclassified the lake from freshwater to seawater in 2001. Construction on a tidal power plant began in 2004 — designed to use the same tidal exchange that was keeping the lake alive, and generate electricity from it at the same time.

The record the plant still holds

The Sihwa Lake Tidal Power Station entered commercial operation in 2011. Its capacity — 254 megawatts — made it the largest tidal power station in the world, overtaking France’s La Rance plant (240 MW), which had held the record since the 1960s.

Capacity
254 MW — world’s largest tidal power station by capacity
Commercial operation
Since 2011
Water quality since
COD back down to around 2 ppm, near pre-seawall levels
Infographic explaining the Sihwa tidal power station: 254 MW capacity, 552 GWh generated annually, completed 2011, a 12.7km embankment; a diagram showing seawater flowing in on the flood tide to spin turbines and generating power, versus sluice gates simply draining the lake on the ebb tide with no generation; ten turbines with 7.5-meter blades; and environmental effects — improved water quality and 862,000 barrels of crude oil imports avoided plus 315,000 tons of CO2 emissions avoided annually
How Sihwa generates power, and what it offsets each year. AI-generated illustration — the figures (254 MW, 552 GWh, 7.5m turbines, 862,000 barrels of oil and 315,000 tons of CO2 avoided annually) are checked against Wikipedia and K-water's own project materials, not invented for the graphic. Photo: Colors Korea, AI-generated · © Colors Korea — AI-generated illustration

The mechanism is simple in principle. The tidal difference between the sea and the lake behind the seawall drives turbines as water moves through sluice gates — the same idea as a hydroelectric dam using a river’s drop in height. What makes Sihwa unusual is the loop it closes: the “problem” driving the design was keeping water moving through a lake that had died from stagnation, and that same motion is what the plant turns into power. Water quality has recovered to close to what it was before the seawall went up.

Standing on top of it

Workers finished the observatory itself in June 2014, a glass-domed tower built directly onto the plant’s own structure. From the deck, the view runs across Sihwa Lake on one side and the open West Sea on the other — the two bodies of water the turbines below are constantly exchanging. On a clear day the causeway road stretches out beneath you in both directions, the seawall and the water it separates laid out at once in a way no ground-level photo of the plant can show.

A separate Sihwa Nare Tidal Culture Center, in the same complex, carries its own exhibition halls. It is worth calling ahead about if the mechanics of the plant interest you beyond the view — hours and programs there run separately from the observatory itself, and the two buildings are easy to conflate from the parking area below.

Getting there

Daebudo has no subway or rail connection — a car is genuinely the practical way to reach the observatory, across the causeway road that doubles as the seawall itself. From central Ansan it is roughly 40–50 minutes by car; public transit means a bus into Daebudo followed by a local connection, considerably slower.

A Korean eSIM is worth having before you set out — live directions matter more here than in the city, and Naver Map handles addresses like this one better than Google Maps does. Our eSIM comparison covers which to buy.

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The coast from here

Quick answers

Is the Sihwa tidal power plant really the world's largest?
Yes, by capacity — 254 megawatts, commercial operation since 2011, ahead of France’s La Rance plant (240 MW), which had held the record since the 1960s.
Why was Sihwa Lake called the "Lake of Death"?
The seawall sealing it off finished in 1994, and with no outlet, pollution from industry and unfinished sewage systems collapsed water quality almost immediately — chemical oxygen demand rose from 2–3 ppm before the wall to about 17 ppm by 1997.
Did the tidal power plant actually clean up the lake?
Water quality has recovered substantially — chemical oxygen demand is back down to around 2 ppm, close to levels before the seawall was built, as the plant keeps seawater moving through what used to be a stagnant lake.
Is the Sihwa observatory free to visit?
Yes — there’s no admission charge, and it’s open year-round, though hours vary by season, so confirm before a long drive out to Daebudo.

Checked 3 September 2026. Observatory hours, admission and address from K-water’s own facility page. The 1994 seawall completion, the collapse in water quality and its “Lake of Death” reputation, the 1997–1999 seawater exchange restoration, the 2001 reclassification to a seawater lake, and the recovery of chemical oxygen demand to around 2 ppm from Korean-language environmental reporting on Sihwa Lake’s history. The tidal plant’s 2004 construction start, 2011 commercial operation, 254 MW capacity and its record ahead of France’s 240 MW La Rance plant from Korean energy-industry reporting and K-water’s own project materials. The observatory’s June 2014 opening from contemporaneous travel reporting. The lead photograph is our own, taken on a visit to the site — this section otherwise relies on KOGL and Wikimedia Commons images, and neither archive had a usable photograph of this particular building. Hours and programs change — confirm before you travel.