The sun’s annual abandonment of northern latitudes becomes evident in the fall. Ice started forming in the bays of Lake Siljan in November, gradually claiming the lake’s surface. Last to freeze – it probably happened in the middle of January – was the main lake basin, called Storsiljan. The ice on the lake typically reaches a depth of about 16 inches.
The winter solstice was over a month ago, and this signals a slow return of sunshine to Sweden. But the lake will hibernate for some time, recumbent. The Grimalkin, this cat-with-the-fish-on-its-back, is reclined on its cold ass.
My effort to swim across Lake Siljan would not be possible without great assistance from Anders-the-son-of-Birger-and-MajLis. More about this later. For now, suffice it to say that Anders has been poking around, asking questions, taking pictures, considering logistics. Anders managed to find some information about historic water temperatures for Lake Siljan. He put me on to a website at the University of Uppsala, where I eventually uncovered a helpful man named Lars Sonesten.
To the extent that I could decipher the university’s webpage, I believe Lars works for the University of Uppsala, at the University of Agricultural Sciences, in the Department of Aquatic Sciences and Assessment.
Lars sent me a large nugget of information, namely a spreadsheet showing water temperature data taken over the last twenty years from four sampling sites across Lake Siljan.
Before reviewing the data, I had thought, anecdotally, that the warmest water would be in late August, or even in early September. But that’s not how it works this far from the equator. The upshot of the data is this: maximum water temperature is historically in the final week of July or the first week of August. By August, sunlight is diminishing significantly enough so that the summertime warming of the lake is at an end. Less sun and colder nights mean that the lake’s warmth will be draining away. Thus I’ll swim between July 25th and August 7th this summer.