Yesterday morning, life-giving mug of coffee in hand, I stepped onto the deck for my usual look-about. The sky overhead was a radiant azure, with faint daubs of gossamer white clouds to the west. A waning quarter moon traced its arcing path toward the horizon. These next few nights will be the final appearances for this year's version of that fabled Harvest Moon; our next full moon, which will occur on October 11, will be the almost equally storied Hunter's Moon.
Time moves steadily on. Just like the river, which last Friday did its astonishing overnight color switch, turning from opaque brown to bright green. This annual phenomenon—so dramatic it's nothing short of natural magic—happens at that point when summer is transitioning onto autumn. The weather cools into the mid-50s for several nights in a row with a concurrent drop in water temperatures.
I've never seen any mention of this sudden "greening" of a stream in anything I've read, so I'm not sure exactly what's going on to cause such an abrupt color change. My best guess is that the water's heretofore impenetrable shade of gray-brown—which, if you didn't know better, might be mistaken for being muddy—is due to some species of algae that's been thriving in the stream's nutritious summer warmth. Then, as the water begins to cool, a critical point is reached which triggers a widespread die-off—like a group of houseplants you forgot to take indoors at night succumbing to frost. That would explain why one day the river is instantaneously a delightful luminous chartreuse—a green so impossible it looks unnatural, as if the water had been colored with dye.
Too, I've noted the peak of this brilliant crazy green lasts only a few hours. By the following day, the color has toned down considerably. This may indicate the glowing temporary green is the color of the dying algae rather than of completely dead plants, and might explain why the green continues to gradually fade over the next couple of months. By mid-November, and on through the heart of winter, the river's clarity is pristine—a colorless mirror which can look blue or gray, gold or black, pink, orange, turquoise or purple, depending on the sky and angle of light.
Today is cloudy with sprinkles. So…no waning Harvest Moon in the morning sky. But the river, now the color of old jade, is whispering the news of seasonal change.