Every fall in the northern Pacific, up to a million salmon migrate back to the rivers and streams where they were born to spawn. Many of these streams are located in Katmai National Park, Alaska. It's here where a massive population of coastal brown bears gather to eat these fish.

Everyone hates biting insects, but if you look closer you can see that even the tiniest and most irritating bug can be essential for a working ecosystem. During a lull in bear and salmon activity, Casey and the crew decide to head inland in search of the spawning fish.