Zengwen River is the fourth-longest river in Taiwan, with a total length spanning 138.5 kilometers and a drainage area of 1,176.7 square kilometers. The source of the river flows from Dongda Mountain in Alishan Township, Chiayi County. The Zengwen River flows through the entirety of present-day Tainan City, eventually flowing into the Taiwan Strait between Annan District and Qigu District. It used to be the boundary between Tainan City and Tainan County, and also a rough boundary between the old urban and rural areas of Tainan City. In the past Zengwen River was nicknamed the "Green Snake" by the residents after four diversions throughout its history. However, the diversion and siltation of Zengwen River over the past century directly contributed to the fertile soils of the Chianan Plains and the present day "Taijiang.”
It was only in the 1930s when Taiwan was under Japanese rule that systematic work began to tame the river. Gradually, embankments were built on both sides of the river to limit the flow of water, which largely resulted in what Zengwen River looks like today. Such environmental changes have created many interesting influences on the religion and culture of the local inhabitants. For example, because of the constant flooding of the Zengwen River, local residents had to carry their houses made of bamboo and migrate during floods, resulting in the stories passed down of villagers moving their whole settlements together. These past experiences have now evolved into a unique coastal settlement culture. Furthermore, the flooding of the Zengwen River created many new fertile lands on which many new settlements were formed by early settlers. Often this is hinted by learning of place names, such as "Shifen,” "Shifenliao,” "Sangu Zizhuang,” "Qigu,” "Xia Shan Zi Liao,” "Wu Kuai Liao" etc. In addition, many of the religious ceremonies and rituals of Taoist temples situated in the river basin have also being influenced by the divergence, flooding, and flow of the Zengwen River, resulting in folk beliefs and fabulous tales of temple-building stories. The temples in the villages are usually religious centers that carry the faith and devotion of nearby residents and is also the center for the dissemination of information and gossip in the settlement. In addition, the Zengwen River flows out into the sea in the estuaries lying between Annan District and Chigu District. Of interesting note is that this is also the area where the three major religious temple processions in Tainan pass through.
Simply put, Taijiang National Park is located on both banks of the lower reaches of Zengwen River. Geologically speaking it is a young environment. The landscape includes a vast stretch of fish ponds, floating lands, lagoons, and various saltwater marshes and other phenomena found in wetland environments. It has become the best wintering place and relay stop for birds migrating through East Asia from around the world. The area around the estuaries has also become a place where many florae with high salt tolerance grow and thrive due to the river water flowing into the sea and the drift of ocean currents, such as plants within the mangrove family, including black mangroves (Avicennia marina), white-flowered black mangrove(Lumnitzera racemosa), which are commonly found here. Other common vegetation includes seaside jack-bean (Canavalia rosea), Taiwan tribulus, shoreline purslane (Sesuvium portulacastrum), herbaceous seepweed (Suaeda maritima), etc. which dot the endless blue waters with patches of greenery. A bird’s-eye view of Taijiang National Park shows countless fields connected, most of which are fish ponds that residents rely on for their livelihoods. This region has a thriving aquaculture industry, with most farmers raising oysters, milkfish, and clams. As a result, this area is often known as “Floating Land of Fish Ponds.".”
The Zengwen River is an important water source flowing through the alluvial Chianan Plain. It has nurtured countless people from the upper reaches all the way to the estuaries leading to the sea. It has also gifted us with picturesque sceneries: "Zengqiao Sunset" was listed as one of the eight beautiful sceneries of Tainan County in earlier times. Even today, the fiery red of the setting sun with the gulf streams in the foreground is still a wondrous sight to behold.