Walden is frozen over.

December 20. 

Walden is frozen over, except two small spots, less than half an acre in all, in middle.

H. D. Thoreau, Journal, December 20, 1858

Walden is frozen over. See December 11, 1858 ("Walden is about one-third skimmed over.");  December 22, 1858 (“The pond is no more frozen than on the 20th.”); December 24, 1858 ("Those two places in middle of Walden not frozen over yet, though it was quite cold last night! "); December 25, 1858 ("Walden at length skimmed over last night, i. e. the two holes that remained open. One was very near the middle and deepest part, the other between that and the railroad.”); December 28, 1858 (“The ice is about six inches thick.”)

See also December 21, 1854 "Walden is frozen over, apparently about two inches thick. It must have frozen, the whole of it, since the snow of the 18th,-— probably the night of the 18th");
December 21, 1855 (“Walden is skimmed over, all but an acre, in my cove.”); December 21, 1856 ("The pond is open again in the middle, owing to the rain of yesterday."); December 22, 1853 ("Walden skimmed over in the widest part, but some acres still open; will probably freeze entirely to-night if this weather holds.”); December 23, 1845 ("The pond froze over last night entirely for the first time, yet so as not to be safe to walk upon”); December 23, 1850 ("Walden is frozen, one third of it, though I thought it was all frozen as I stood on the shore on one side only"); December 24, 1856 ("Am surprised to find Walden still open in the middle.”); December 24, 1859 ("There is, in all, an acre or two in Walden not yet frozen, though half of it has been frozen more than a week"); December 26, 1850 ("Walden not yet more than half frozen over."); December 26, 1853 ("Walden still open.. . . the only pond hereabouts that is open."); December 27, 1852 ("Not a particle of ice in Walden to-day. Paddled across it.);  December 27, 1856 "Walden is still open in one place of considerable extent, just off the east cape of long southern bay.");. December 27, 1857 ("Walden is almost entirely skimmed over. It will probably be completely frozen over to-night");. December 28, 1856 ("Walden completely frozen over again last night."); December 29, 1855 ("Am surprised to find eight or ten acres of Walden still open,. . .It must be owing to the wind partly.");December 30, 1853 ("The pond not yet frozen entirely over; about six acres open, the wind blew so hard last night. "); December 30, 1855 ("There was yesterday eight or ten acres of open water at the west end of Walden, where is depth and breadth combined"); December 31, 1850 ("Walden pond has frozen over since I was there last."); December 31, 1853 ("Walden froze completely over last night. It is, however, all snow ice, as it froze while it was snowing hard, and it looks like frozen yeast somewhat.”)

Thursday. December 20 It is in the 40s we go out after sunset and take one of those new routes off the rocky trail. The one with the steep climb through rock garden of moss and ferns. The moon will not be full for a couple of days and is concealed by clouds. With the snow cover it is light enough to walk without headlamp (except we use the red light) I read later from Henry’s journal of August 5, 1851“When the moon is on the increase and half full it is already in mid-heaven at sunset so that there is no marked twilight intervening”  and December 10, 1856("The nights are light on account of the snow, and, there being a moon, there is no distinct interval between the day and night.") This seems to be the case tonight. I sit on the bench and look out over the lights in the valley. There is a forecast for rain in 88 minutes so we do not linger, walking back down along the edges of the rocky trail in the crusty snow then heading north to cross the stream and back along the ridge and out.  It begins to rain lightly. ~ zphx 20181220