To keep Tokyo high and dry, management of local river and water resources has been always been a key concern, and to this key, Kita Ward holds the locks. Sluice-gate locks, that is.
Residents of the Kita area once built mizuya (homesteads perched on flood mounds) and surrounded their yards with bamboo fences to retain any belongings or family members that might otherwise float away when the Arakawa ("wild river") surged with rain. Edo folk living downstream, in quarters too close to make flood mounds practical, were periodically deluged with mud, left homeless and injured, or worse.
After one catastrophic flood in 1910, which displaced over a million people, the government decided that the Arakawa should be tamed. Construction of a massive drainage canal began, and a lock system was designed to control the water levels of the Sumida River, protecting the city to the south. Kita Ward's Akasuimon (Red Sluice Gate) at Iwabuchi was completed in 1924, just above where the Shingashi River joins, and marks the current day starting point of the Sumida River. Designed by Akira Aoyama, who drew on his experience as a Japanese architectural consultant (and the only one at that) on the Panama Canal a decade earlier, the brilliant red lock is one of the ward's most compelling sights.