Uncle John's Band

From the song of the same name by the Grateful Dead, and released on their 1970 album Workingman's Dead.

Most of the lyrics are a bit mystical, and don't concern the titular band. What can be determined is this band has a regular gig playing an estuary, where a river meets the ocean:

Come hear Uncle John's Band by the riverside,

Got some things to talk about, here beside the rising tide.