Perhaps the best-known salmon runs in the world happen every summer in Seattle at the tourist- and locals-thronged Ballard Locks. Right now, sockeye salmon are climbing the concrete ladders that separate Puget Sound’s saltwater from the fresh water of the ship canal that leads to Lake Washington and the spawning streams beyond. 657 fish made it through yesterday.

The Lake Washington sockeye must be the most urbane tech-savvy salmon anywhere. Departing young fish are jettisoned into the Sound through high-tech smolt slides. Upon their return, years later, some are tagged with sensors to measure water temperature. Others carry receivers that allow researchers to count how many make it out of the ship canal. And still others get receivers to measure the number that make it to spawning grounds. You can even watch a 30-second movie of them passing through the Locks. No doubt by next year, biologists will be giving them salmon-friendly i-pods.

But while researchers are predicting that 400,000 sockeye will swim through Seattle’s urban heart this summer, they are increasingly worried about another major die-off, like the one that happened last year when roughly 200,000 salmon mysteriously died between the Locks and the spawning beds. The best available explanation is unseasonably warm water temperatures that resulted from warmer-than-average weather.

The route from the locks to the lake is thick with urban perils. But most problematic for the cold-water loving fish: the way is often shallow, narrow, and warm; and that warmth can weaken immune their systems and even kill the salmon outright. In fact, new research finds that Lake Washington surface-water temps have risen by about 4 degrees in the last 35 years; and most of that increase is attributed to hotter air. It’s not surprising then that three of the four biggest salmon die-offs between the locks and the spawning grounds have occurred since 2000.

The sockeye, which may be suffering the effects of global warming, are Seattle’s canaries in the coal mine of climate change. (If by canaries you mean fish, and by coal mine you mean waterways. But whatever.)