Sockeye return to spawn in B.C.'s Adams River every year, but every fourth year, there is a dominant run in which the number of fish increases dramatically.
In off years, sometimes only a few thousand fish return, but on a dominant year, three million or more can crowd into the river, triggering a Salute to the Sockeye festival that draws tourists from around the world.
In 2010, when more than 3.8 million fish returned, the festival, organized by the Adams River Salmon Society, broke attendance records with about 230,000 visitors during the three-week event.
This fall, with about two million sockeye returning, the festival seems well on its way to matching those visitor numbers, with crowds gathering on viewing platforms to watch salmon schooling or pairing up to mate. The festival ends Sunday, but the salmon, running late this year, will be spawning for weeks.
The sockeye, which have bright red bodies and green heads, stand out vividly in the clear waters. And because the fish often stay near the riverbank, tourists are almost close enough to touch them.
Each female salmon builds several nests, collectively known as a redd, and a male, who has lain close to her for days fighting off rivals, releases his sperm just upstream. He drifts away to die while she guards the nests for a few more days, until she too grows weak and dies.
Dead or dying salmon stack up at the river mouth or collect along gravel bars, with flocks of gulls wheeling overhead. Fisheries and Oceans Canada workers in rafts tag salmon to help determine the number of spawners. The full count won't be known for several weeks.
"I think it's going to be a very good run," says Mike Lapointe, chief biologist at the Pacific Salmon Commission. "It's an awesome place, and I'm glad it's there."