The Moneans were a spacefaring humanoid species from the Delta Quadrant. Originally nomadic, in the 21st century they discovered and settled on an artificially coherent planetoid of water, which they termed the Waters. Their government was the Monean Maritime Sovereignty.
Although they had built an industrial infrastructure and undersea dwellings, most Moneans still chose to live as their ancestors did, aboard ships. The Moneans possessed limited knowledge of the deep regions of their home, as their best research vessel could only dive 100 kilometers while the Waters' center was 600 kilometers deep. Unfortunately, the ocean eventually began to lose containment, at a rate that would have resulted in its complete dissipation by 2380.
In 2375, the USS Voyager encountered the Moneans. Tom Paris, Seven of Nine and Monean scientist Riga embarked on an expedition on the Delta Flyer to investigate the containment loss. They discovered an ancient field reactor at the center of the ocean, and learned that the Moneans' oxygen refineries was increasing the ocean's density, forcing the reactor to divert energy from containment to its own structural integrity field.
From their findings, Riga recommended that the Moneans immediately reduce their rate of oxygen extraction, while Voyager offered to share replication technology so they would no longer have to remove it from the water. However, the Monean bureaucracy was reluctant to make such sweeping changes. Riga and Paris, acting against orders, attempted to take matters into their own hands by destroying the oxygen refineries, but they were stopped by Voyager. (VOY: "Thirty Days")