The lock is a gate that connected the differing water levels of the Yodogawa and Okawa rivers so that boats could pass through. When the Yodogawa River underwent improvement work during the Meiji period, it was installed along with a weir which adjusted the volume of water in the river. It is no longer used; however, it has been preserved as a historic industrial site that is open to visitors. The large and small stones placed around the Yodogawa River renovation monument are known as “Unfortunate Stones.” These stones were carried on the river from Fushimi when Osaka Castle was rebuilt during the Edo period but fell off the barges and could not be used in the castle walls. They were later dredged up during the Yodogawa River improvement project and placed here.