The Tama River trail is one of the best ways to go on a long, uninterrupted run in Tokyo. Though not right in the central city, it is easily accessible along most of its length via subway. This trail is also popular with cyclists. One can run all the way from Fussa station line in the north, heading south toward the sea. The paved path parallels the river most of the way, slightly above the river. There are some sections where a gravel trail runs level with the river, and some sections where there is a path on both sides of the river.
We’ve mapped out a slightly over 10k loop between Numabe and Futakotamagawa stations. It is ~30k from Fussa Station on the JR Om line to Futakotamagawa station on the Oimachi and Denentoshi lines, and then another ~12k or so to the sea.