Garfield Cat is correct. Egret park is the new end of the upper section of the LARIO path. That is basically where San Fernando Road meets Ave 26, near the LA River Center, and just east of Dodger Stadium. There is supposed to be a few more miles of park added in Glendale north of Griffith Park, but I am not sure when that will open, or if the bike path will continue there.
The river ride's path is fairly circuitous through Boyle Heights, Chinatown and then into Lincoln Heights/Cypress Park so it may be possible to find a quicker way.