Yantlet Creek is the creek draining into the River Thames that separated the Isle of Grain from the Hoo peninsula. It once connected the River Medway with the River Thames and made the Isle of Grain a true island. The creek silted up and now drains the area of The Isle of Grain and Allhallows Marshes. A monument known as the London Stone is located at its mouth and marks the limit of the City of London's ownership of the Thames. Yantlet gives its name to the Yantlet Reach on the Thames, and in its time has been used as point where the river became the estuary.