Wushantou Reservoir & Hatta Yoichi Memorial Park

Wushantou Reservoir (烏山頭水庫), also known as Coral Lake (珊瑚潭) for its intricate shoreline, is located in Guantian District, Tainan, Taiwan. It forms the heart of the Chianan Irrigation System (嘉南大圳), which was the largest irrigation network in East Asia when completed in 1930. The system comprises over 16,000 kilometres of irrigation and drainage channels serving 150,000 hectares of farmland across the Chianan Plain.

The project was designed by Hatta Yoichi (八田與一, 1886–1942), a civil engineer from Ishikawa Prefecture who was dispatched to Taiwan in 1910 after graduating from Tokyo Imperial University. Construction began in 1920 using the semi-hydraulic fill technique — a method so rarely employed that Wushantou is often described as the only dam of its type remaining today. A diversion tunnel was also constructed to channel water from the Zengwen River into the reservoir. At completion, the dam stood 56 metres high with a storage capacity of 150 million cubic metres.

The Chianan Irrigation System revolutionised agriculture on the Chianan Plain through its innovative three-year crop rotation system, enabling three times as many farmers to benefit from irrigation. This dramatically increased rice and sugarcane output, making Taiwan a critical food and sugar supplier for the Japanese Empire. During the Second World War, the agricultural productivity enabled by the system was vital for sustaining Japan's wartime economy, with Taiwan serving as a major source of rice and refined sugar for the military.

Hatta Yoichi was dispatched to the Philippines in May 1942 to survey irrigation for cotton cultivation, but his transport ship, the Taiyō Maru, was torpedoed by the American submarine USS Grenadier and sank on 8 May 1942. Hatta perished at sea. His wife, Toyoki, had evacuated to Wushantou late in the war; on 1 September 1945, shortly after Japan's surrender, she took her own life by throwing herself into the outlet works of the reservoir her husband had built. During the war, local residents hid Hatta's bronze statue to prevent its confiscation for military metal drives; it was found after the war and in 1981 was set on a new pedestal in front of the couple's grave.

Today the site operates as Wushantou Reservoir Scenic Area and includes the Hatta Yoichi Memorial Park, which was renovated and opened in 2011. The park preserves four restored Japanese-era residences, including Hatta's own home, a Japanese garden, and the bronze statue and tomb of Hatta and his wife. The reservoir remains in active service for irrigation and is a candidate for UNESCO World Heritage listing. An annual memorial ceremony is held every 8 May, attended by Japanese and Taiwanese dignitaries.