Every spring, gray whales flock to Oregon's Pacific coast. The nutrient-rich waters here make for a great stopover en route to their southern breeding grounds, but the leviathan layover brings something else along with it: hungry orcas.

While the orcas' presence is nothing out of the ordinary, one killer whale made quite a spectacle of itself this week by swimming up a coastal river. 

Surprised by the sighting, local resident Deborah Heldt Cordone recorded the whale as it swam past her Siuslaw River home. Speaking with local news station KVAL, Heldt Cordone explained that the whale navigated an impressive two miles of river before making an about-turn and heading back towards the sea.  

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The orca swam about two miles up the river before heading back out to sea. 

Some have expressed concern for the orca's safety, but it's important to note that is not a freshwater estuary. Though it is possible for a large animal to be trapped here by low tide, this whale was in no immediate danger.

In fact, the behaviour has been seen before. Just last year, a small pod of killer whales was spotted taking a similar tour of the river. It's a rare occurrence, but that doesn't mean the animals were lost. Like most things in the natural world, there is a logical explanation for the whales' decision to cruise into the river mouth: travelling up the Siuslaw brings the promise of food.

Some killer whales (known as "residents") eat fish, but "transients" like these orcas typically feed on marine mammals. They may be in Oregon in search of gray whale calves to feast on, but trapping seals and sea lions against the shallow riverbed also makes for easy hunting. 

"Before they showed up there were seals around," explained one onlooker. "Then all of a sudden the seals were gone."

While this year's river visitor didn't seem to make off with a catch, it certainly put on a show, breaching several times before making its exit. Keeping a safe distance between their boat and the whale, a pair of fishermen followed slowly behind to look for any signs of trouble. After a quick tail lob, the animal swam over the sandbar and back into Pacific.

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Top header image: karen, Flickr