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Groundwater seeps: the patches of woods that never freeze

November to March

Where groundwater reaches the surface at a seep, it arrives at close to the average annual temperature of the ground rather than the temperature of the air, so it keeps trickling and the mud stays soft while the pond and the brook edges ice over. After a hard freeze it is the one dark, wet, moving patch in a frozen wood.

Why this time of year

A seep does the same thing in August that it does in January; what changes is everything around it. Once a hard freeze has locked up the still water and skinned the edges of the brooks, the seep stops blending in and becomes the most obvious thing on the hillside, which is why this card waits for the cold rather than for a date.

How to notice it

  1. Go a day or two after a hard freeze, when the still water has iced over and there is frost or snow on the ground.
  2. Work along the base of a wooded slope, or a bench partway up one. Seeps come out where the water table meets the surface, usually at the foot of slopes and in coves.
  3. Look for dark, bare, saturated ground, a thread of open running water, or a patch of green moss in a landscape that has neither.
  4. Stand at the edge and look, do not walk in. The giveaway is that the ground there is soft when everything around it is hard.

Try this with kids: Everything out here is frozen except one muddy patch that is still running. Where is that water coming from, if it is not coming from the sky?

a seep is a place where groundwater comes out over a broad patch of ground rather than from one spring mouth

Safety

  • Ice at the edge of a seep or a spring-fed trickle is thinner and far less predictable than ice on still water nearby, because moving water thins ice. Do not test it by standing on it.
  • The unfrozen ground at a seep is saturated mud that grabs boots. Keep children at the edge rather than in it.

Sources

  • northernwoodlands.orgNorthern Woodlands, the mechanism verbatim: springs take on the average annual air temperature of their locality, and Big Spring's water measures 41 degrees in midwinter, just as it does in August. Also that groundwater-fed springs can flow year-round, regardless of plunging temperatures that layer thick ice on surface water streams, and it closes by telling the reader to go and find exactly this. The 41 degrees is Mount Mansfield's instance of the rule and is NOT offered here as a Massachusetts figure.
  • vtfishandwildlife.comVermont Fish and Wildlife, verbatim: this flow continues through the driest summer months, and in winter, warms the soil and prevents freezing; groundwater in our region is typically about 47 F and varies only a few degrees from this temperature; the mucky surface organic soils may not freeze during the winter because of the constant input of relatively warm groundwater; and machinery should be kept out of woodland seeps. The 47 F is Vermont's regional number and is deliberately NOT used as a Massachusetts figure on this card. Returns 403 to a bare curl and 200 to a browser user-agent.
  • extension.unh.eduUNH Cooperative Extension: seep waters may remain underground for many years, producing clean waters and warmer temperatures than typical surface waters in winter and cooler than typical in summer, and their flow may keep the water from freezing during winter and they are the first to green up in the spring. This page is also why the card makes no claim about midwinter green growth.
  • vtfishandwildlife.comVermont Fish and Wildlife, for the first safety note only, verbatim: be extremely cautious crossing ice near river mouths, points of land, bridges, islands, and over reefs and springs, because current almost always causes ice to be thinner over these areas. See notes: this is a lake-ice press release and is being used for the physical principle, not for its setting.

Checked against these sources on September 13, 2026.

In the guide for November, December, January, February, March

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