Reisenjima - Wasabi Fishing?

This has to be one of the lowest rate items I have ever tried to fish. Does anyone have advice for success? Using Lu Shangs + Robber Rig, have also tried Rogue Rig.

Edit: As a note; I have been fishing at the South water fall but much greater luck at the North waterfall, near the 2 frogs, conflux 4.