In the annals of climate change you can record another notable event. The Fraser River is running hotter and lower in the first week of July than it usually does in the dead of August.

The water temperature is currently about 19 C, the level at which salmon start to show physiological stress, and the flow has dropped to extreme lows.

“These flows are definitely lower than anything we’ve experienced and I’d say the temperatures right now are warmer than anything [on record for July],” said Mike Lapointe, chief biologist for the Pacific Salmon Commission (PSC).

“I just looked this morning and went ‘Gee, it looks like the temperature at Hope is right around 19’ and I think it was as high as 19.5 a few days ago. That’s ridiculously high for this time of year,” he said.

Usually, the river is still swollen with snow melt and is typically about three degrees cooler. But with the snow pack long gone, and a record hot, dry June melting into an unusually warm July, Fraser River salmon are facing tough conditions.

Research in recent years, much of it led by the Department of Fisheries and Oceans and the University of British Columbia, has shown that the swimming performance of migrating salmon begins to decline when water temperature hits 18 C. At 19 C, there are early signs of stress and the fish start to slow their upstream migration. At 20 C, fish start to die in the river and there are disease outbreaks. In some hot summers, 40 per cent to 90 per cent of salmon have died in the Fraser before they have the opportunity to spawn.

Fewer people are watching the current conditions with more concern than Mr. Lapointe, who constantly monitors the Fraser’s salmon runs and advises the PSC on the status of stocks. He knows that if conditions don’t improve, plans to open the river to salmon fisheries this summer may have to be cancelled.

While the earliest arriving sockeye should start to show up in the river this week, the bulk of the run won’t come in for another month. The temperature could cool by then and rains could increase flows. But right now, things don’t look good.

“It is definitely warmer than normal and flows are well below normal … and if that persists … it’s going to put us in a very difficult situation come [August] when we consider whether or not to have any kind of fisheries,” he said in an interview.

“I hope it rains.”

The only thing the PSC can do if the poor migration conditions persist is to assume a high rate of mortality, and then regulate the commercial, First Nation and sport fisheries in the river accordingly.

In other words, if a large number of fish (possibly hundreds of thousands) are expected to die because of warm water conditions, the catch will need to be restricted. And it is possible no fishing at all will be allowed.

“We can’t do anything more than minimize the impact of the fisheries and if that’s what we have to do I’m confident that’s what the [PSC] panel will do because they are fairly used to doing that, unfortunately, in the past 10 years or so,” said Mr. Lapointe.

He said the Fraser has experienced 10 of the warmest years on record over the past 15 years and the trend is driven by climate change.

What that means to salmon in the long run isn’t clear. There is some hope fish can evolve to cope with warm water, but can that happen fast enough?

“I do think they will evolve, but that’s the question: how fast will the fish evolve relative to how fast will the climate change?” said Mr. Lapointe.

He says it is likely some stocks will collapse, while others might adapt and thrive.

That means fisheries managers have to be extremely cautious, because the last thing they want to do is allow fishermen to kill fish that could hold the genetic key to the future of the species.

The hot spell will end eventually, but the concerns about fish won’t evaporate when the rains come. The climate is changing and unless salmon do too, they might vanish.