Boiling point: Hot water killing 50% of Columbia River’s salmon population

The Columbia River in Oregon and Washington is usually teaming with hundreds of thousands of sockeye salmon this time of year, but warming waters have wiped out nearly 50 percent of this year’s population – and it could get worse.

Although more than 507,000 sockeye salmon have migrated up the Columbia River this year, more than 250,000 have died, according to the Associated Press. Reuters, meanwhile, put the number at 235,000.

“We’ve never had mortalities at this scale,” said Oregon Department of Fish and Wildlife fisheries manager John North to Reuters.

In fact, the bad news could get even worse: Up to 80 percent of the entire population could ultimately die, Ritchie Graves of the National Oceanic and Atmospheric Administration told the AP.

The enormous mortality rate has been blamed on water temperatures reaching up to 76 degrees Fahrenheit. Scientists say that water temperatures above 68 degrees can put severe stress on fish, since there is less dissolved oxygen to be found in water at higher temperatures. This makes it hard for the salmon to breathe, an issue that becomes especially serious since their metabolism also spikes under such conditions, forcing them to burn off energy that would otherwise be saved for later.

Additionally, hot water can foster the growth of deadly pathogens that can infect the fish.

“The water temperatures in the Columbia River are nearing lethal levels for salmon, which is a little inconvenient if you’re a salmon trying to come into the Columbia River and migrate,” Teresa Scott, Washington Department of Fish and Wildlife’s drought coordinator, said to ThinkProgress. “It’s a matter of fish being caught in those warm waters and not being able to deal with them.”

Contributing to the warmer water is a combination of drought conditions on the West Coast and higher than normal temperatures, as well as unusually low runoff from mountain snowmelt. Snowmelt can help keep rivers cool, but this year the Columbia River reached 70 degrees in the middle of June, Reuters reported. It doesn’t typically hit that level until mid-July.

In an attempt to help, officials are unleashing cooler water from various reservoirs into the river to keep temperatures at a more manageable level for the fish. Another option is pulling the fish out of the river and trucking them to cooler waters.

Still, Scott said that low snowmelts and high temperatures could be a continuing problem if the climate keeps getting hotter.

“There’s no doubt on the part of our climatologists that say that these are the kinds of conditions that we will see in the future,” Scott told ThinkProgress. “We are mounting short term responses this year, and anticipating a recovery from these conditions in the near term, but certainly this is a wakeup call and a dress rehearsal for what fishery managers years from now will be dealing with on a regular basis.”