WENATCHEE — It’s as much a hallmark of the changing seasons in North Central Washington as the coloring of the leaves and the drop in temperatures.

Every fall about this time, thousands of enormous summer chinook salmon return to local waters after their multi-year journey to the ocean and back lay eggs to complete their life cycle and then die. As they splash through shallow riverbeds to dig nests and chase off other salmon to protect them, the show often draws crowds of onlookers to the riverbanks.

“This is what people are coming to see in all the canyons this time of year,” said Todd West, fish and wildlife superintendent for the Chelan County PUD. “You can practically stand next to a 30-pound salmon doing its thing in the river.”

Over the next two weeks, the numbers of spawning salmon will peak and create what West calls a “carpet bombing” effect in some areas. “There will be so many chinook, that you’ll have redds (nests) on top of redds, and the whole bottom of the river will be turned up,” he said.

He said the nests are easy to spot. The giant fish scour out the rocks to create what looks like white horseshoe-shaped nurseries to deposit their eggs on the river bottom.

“If you look closely, you’ll see the male and female close to their nest guarding it from other fish,” he said. “They are very territorial around their nests.”

The PUD has been surveying the salmon spawning grounds in the Wenatchee River annually for more than 20 years.

For seven weeks each fall, the agency’s wildlife experts travel the entire length of the river in rubber rafts, counting salmon and mapping the nest sites. Hundreds of nests are tallied by early November.

The PUD crew starts the journey each Monday, traveling from Lake Wenatchee to Shugart Flats near Plain. On Tuesday, they continue on to the Tumwater Bridge. On Wednesdays they typically make it as far as the mouth of Icicle Creek. Thursdays take them to the Peshastin area. Then Friday they travel to the confluence with the Columbia River.

Then they repeat the route the next week, typically ending after the first week of November.

The idea is to track the progress of the spawning salmon and gauge the viability of the local population, West said.

So far this year, just over 44,000 adult summer chinook salmon have been counted at Rock Island Dam, nearly double the 24,222 yearly average for the last 32 years, according to the federal Fish Passage Center.

Three races of chinook salmon spawn in local waters. Spring chinook spawn earlier in the fall, and choose nesting sites in upper reaches of river systems. In the Wenatchee drainage, they spawn in the Little Wenatchee, White and Chiwawa rivers. The summer chinook come next, and spawn in the river below Lake Wenatchee. The fall runs tend to spawn in the Columbia River, West said.

While this year’s run of summer chinook appears to be strong, West cautioned that a high nest count does not guarantee a big return in a few years. Falls rains can still mess it all up. Heavy rains can cause the river to swell and either wash out the nests or smother the eggs with silt. The population can take a dramatic drop in the years after a big flood, and had dipped as low as 6,300 over the last 30 years.

“A muddy Wenatchee River can wipe out the fish run,” he added.

Overall, though, the population is considered healthy, and the fish are not protected by the federal Endangered Species Act.

“We’re pretty fortunate that we have a very good summer run most years,” West said.

Michelle McNiel: 664-7152

mcniel@wenatcheeworld.com