A more thorough explanation:

Definition: Innavigable (in-nav-i-gə-bəl) is an adjective used to describe a body of water that is not suitable for navigation or a vessel that is unfit for service.

Examples:

• The river was innavigable due to the large rocks and rapids.
• The ship was deemed innavigable after it suffered severe damage in a storm.

The first example illustrates how a body of water can be innavigable due to natural obstacles such as rocks and rapids. The second example shows how a vessel can become innavigable due to damage or other factors that make it unfit for service.