Original: The name Hydra was announced on June 21, 2006, in IAU Circular 8723, IAU Circular No. 8723 naming the moons along with the formal designation Pluto III.
Simplified: The name Hydra was announced on June 21, 2006, in IAU Circular 8723IAU Circular No. 8723 naming the moons, along with the formal designation Pluto III.