Located at the headwaters of the Laojie River, Longtan Lake is one of Taoyuan's most important recreational and environmental assets. Over time, wastewater, agricultural runoff, tourism pressures, and limited natural inflows led to deteriorating water quality, algal blooms, and poor circulation. To help restore the lake and its upstream waterways, the Taoyuan Department of Environmental Protection engaged our team to plan and design an integrated water quality improvement and waterfront revitalization program.
At the heart of the project is Taiwan's first multi-soil-layering (MSL) water treatment system, a nature-based technology that we adapted from Japan to local conditions. Using soil, gravel, carbon, and iron media, the system removes pollutants without chemical additives, reducing operational requirements and minimizing secondary pollution.
The facility treats up to 18,000 cubic metres (635,664 cubic feet) of water per day by intercepting upstream flows and recirculating lake water through the treatment process. This reduced the lake's water renewal cycle from approximately 200 days to just 7, improving circulation, lowering nutrient levels, and helping control algal blooms. At completion, it was the first MSL facility in Taiwan and the largest of its kind in Asia.
Built underground to preserve the surrounding landscape, the facility enabled the creation of accessible green space, waterfront trails, ecological corridors, habitat enhancements, and educational features. Longtan Lake demonstrates how nature-based solutions can improve water quality, strengthen biodiversity, and create lasting value for the community.
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