Although most DIII-D plasmas are stable to the fishbone instability, fishbones are sometimes observed when βp ≳ 1.5 and e ⪅ 5 × 1013 cm−3. These bursts are usually of minor significance operationally; however, under one condition, over 50% of the beam power was lost. The angle of beam injection has little effect on the virulence of the instability, suggesting that the fishbone instability in DIII-D is the ion diamagnetic branch of the internal kink.