Kokyo Gaien Moats

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Kokyo Gaien Moats

The 12 moats around the Imperial Palace make Kokyo Gaien the most important freshwater habitat for wildlife in central Tokyo. Human intervention in the 0.37 square kilometers of moat cover is kept to a minimum, allowing diverse flora and fauna to thrive.

The moats were once both a line of defense for Edo Castle and a means to transport goods. Today, they are an important aquatic ecosystem and a popular place with people who come to walk and relax. Chidorigafuchi Moat, in particular, is a famous scenic spot. During cherry blossom season, its cherry tree-lined path makes it one of the most popular viewing spots in the city. The moats are home to about 25 species of local fish, including stone moroko (Pseudorasbora parva), as well as freshwater shrimp (Macrobrachium rosenbergii). Insects and birds thrive here, and in winter, migratory birds, including tufted ducks (Aythya fuligula) make the moats their home. Several nonindigenous, introduced fish species, including bluegill (Lepomis macrochirus) also live in the moats, posing a threat to native species.

A water-purification system and pumps were installed in 1995 to keep the moats cleaner. The system processes around 20,000 cubic meters of water per day from many of the moats. This improvement has had an immensely positive impact, making them cleaner, clearer, and allowing sunlight to reach the bottom, encouraging new plant life to grow. At night, they are remarkably dark, in stark contrast to the rest of the city. Low-key lighting is a deliberate measure to protect and ensure minimal impact on the wildlife along the moats.