Sumiko III was a planet, home to an Emerald Wading Pool. It was presumably located in the same system as Sumiko IV.
A simulation of the pool was available aboard the USS Enterprise-E in 2373. (Star Trek: First Contact)
- Sumiko III was described as the location of the Emerald Wading Pools in the script of Conundrum, as an alternative to the Cliffs of Heaven on Cirrus IV. In the actual episode the references got mixed up and the crystal pools were now located at Cirrus Four. However, a reference in First contact apparently sourced the script and thus canonised Sumiko III as another location of an Emerald wading pool, after all.