Also located at the Continental Divide is ISA LAKE. In the early days of the exploration of the American west, Indian guides were often used to lead the way. When the explorers first reached the apex of the country, the Continental Divide, they asked their guide, Nantuka, whether the body of water at the divide was a lake or a river. Now, unlike most Indian guides, Nantuka had a fluent command of the English language. So, in very proper English, he replied, "This is a lake." The explorers, not being accustomed to their guides being so articulate, and not being accustomed to the use of verbs and adjectives from the Indians, took Nantuka's response as, "This Isa Lake." Thus, ISA LAKE was born.

It should be noted, however, that other, less embellished accounts, merely indicate that Hiram M. Chittenden, the discoverer of the lake, named it after Isabel Jelke.