Guide

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How vernal pools fill back up after a dry summer

November to March

A vernal pool is a small woodland hollow with no fish that is usually dry by late summer and starts holding water again after late fall rain, filling most with spring rain and snowmelt. The leaf-filled dip you passed dry months ago may be holding standing water again, waiting for frogs and salamanders.

Why this time of year

Once the leaves are down and the trees stop drinking from the ground, rain and rising groundwater start to fill the dry hollows again. How full a pool is depends on recent rain and snowmelt, so some pools start filling in fall and others not until spring.

How to notice it

  1. Walk back to a woodland hollow you saw dry earlier in the year, or any low spot in the woods with no stream running through it.
  2. Look for standing water lying over the leaf litter, with no stream flowing out of it. Note how far it spreads and where the edge sits.
  3. Look at the water for fish or a stream. There should be none, which is why it suits wood frogs and mole salamanders.
  4. Come back after more rain or a thaw and see whether the edge has moved. A pool that is frozen over is still a pool.

Try this with kids: Which leaves are underwater? Can you find the edge of the pool and put a stick there to see if it moves?

Phrase to know: A “vernal pool” is a seasonal woodland pond that dries out most years, so fish cannot live in it.

Safety

  • Stay off the ice on a vernal pool.
  • Look from the edge and do not wade or collect anything.

Sources

  • nrs.fs.usda.govUSFS-hosted book chapter by Leibowitz and Brooks (Hydrology and Landscape Connectivity of Vernal Pools). Quote: 'Geographically isolated pools in this area [central Massachusetts] are typically dry or at minimum depths by the first of October, fill partially with late fall rains after leaf fall, fill to capacity with spring rains and snow melt, and then dry through late spring and summer'. Also: 'a pool can be dry or full to overflowing in almost any month'. Colburn: 'Short-cycle, fall-filling pools behave similarly, except they fill in late fall or early to mid winter.'
  • vernalpool.orgVernal Pool Association (Mass-based). Pool fills 'with the rising water table of fall and winter' and 'the meltwater and runoff of winter and spring snow and rain'; many Northeast pools are ice-covered in winter; late summer pool usually dry.
  • naturalheritage.dcnr.pa.govPennsylvania Natural Heritage (regional analogue, not MA): 'Some fill with fall and winter rains, while others require larger amounts of snow melt and rain in the spring.'
  • research.fs.usda.govUSFS study of 34 central Massachusetts pools: surveyed 'in early spring when the pools were at maximum extent after receiving snowmelt runoff' (supports spring max fill; page says nothing on fall).

Checked against these sources on October 13, 2026.

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

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