You can’t quite prepare yourself for the amazing sight of thousands of salmon heading upstream to spawn. That’s because they do not travel, la di da, to their spawning spot. They fight for it.

I observed this natural show this week in Ketchikan, Alaska, a historic town of about 8,000 people, and a popular cruise port on the Inside Passage. (I arrived in town on a Royal Caribbean ship.)

The lifecycle of a salmon goes something like this: They're born in freshwater streams, head out to sea, and at the end of their lives they return to the place of their birth to lay and fertilize eggs. The roundtrip is thousands of miles. Why they do this is a secret of Mother Nature.

This time of year, on the stream that runs through Ketchikan's colorful historic district, there's only one main event: the Coho salmons' return. The fish, which commonly weigh 4 to 10 pounds, look enormous, even when viewed from a boardwalk area well above the river.

To get up the salmon ladder (a rapidly flowing waterfall that leads upstream), the fish jump and struggle against the current, bounce off each other and do what looks like a fish version of nuzzling for encouragement. Or maybe they are pushing and shoving? It’s hard to tell.

Some fish head up the center of the rapidly flowing water, while others choose the shallower, rockier sides. Only one-third will make it. Those that don't make it die, and those that do die too, after they spawn. Before you feel badly, remember they then become food for the resident bear and eagle population.

You can see the fish from many sites in town, but the best viewing is off historic Creek Street (which had as many as 30 brothels that catered to fisherman in the early 1900's). Look for "Married Man’s Trail."

Guest blogger Fran Golden is co-author of Frommer’s Alaska Cruises & Ports of Call