Argo (planet)
Argo was an inhabited planet and the homeworld of a humanoid species known as the Aquans. Other life forms included algae, fish, and the sur-snake. Plant life included sea foliage and plants reminiscent of trees on land.

Once a land planet, Argo's surface became almost completely covered by water following a series of violent seismic disturbances, leaving only a single large land mass and some outcroppings suggesting the peaks of submerged mountains. At one point, an entire portion of a continental shelf sank within minutes. At least one sea quake occurred in the 23rd century, which the Aquans considered evocative of legends about the cataclysm.

The underwater landscape included at least one reef barrier. Its north polar sea was completely uninhabited.

As of 2269, the planet had undergone several surveys, but still almost completely unexplored and the existence of the sur-snake or the Aquan civilization was unknown. In 2269, the  visited it on a mission to study the effects of the quakes and other phenomena the planet had on its surface. With that knowledge, they hoped to save millions of lives on a Federation planet identical to Argo that was soon to be undergoing a similar seismic transformation.

After not only learning how to redirect the seismic disruptions but also applying a technique for doing just that which employed the Enterprises weapons, some of the land that had previously been under water was returned to the surface. This land included an ancient city of the air-breathing ancestors of the Aquans. The young Aquans planned to restore the shelters therein. ()

Appendices

Background information 
According to Star Trek: Star Charts (p. 27), Argo was classified as a O class planet.

Apocrypha 
According to The Worlds of the Federation, Argo was the first planet in the  system and the Aquans referred to it as "Hestalor." Argo was classified as an N class planet.

External link 
 

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