Didn't know that was a cover till 4-5 years ago.
Saw Canned Heat do it at an all day festival in the 70's. Starstruck was the band right before them. (They did "Black Betty", also a cover) and came out and played with The Heat.
I remember the peeps in front of me looking at me funny when I shouted, "Bullfrog Blues". Then they played it.