The Road From Atlantis

The Montana is directed to assist a species on the edge of extinction...

The amphibian inhabitants of Amithian are dying. Their ancient sun has become a Red Giant, causing a drought and famine that has lasted four hundred years, killing millions.
The Amithian's entire civilization is based on water, it provides their food and fusion power. As their oceans dry and turn to dust the last few thousand survivors must find a new home world or face the end of their existence.
Desperate and dedicated research has brought them Warp technology and, with their first forays into space, contact with the Federation, who has agreed to assist them in their search.