Vernal pool in winter. Many pools fill in fall or winter. Frozen ground helps retain water produced by rains or melting. Vernal pools are easily visible when ice-covered in the leafless forest. Vernal pool in spring.
Vernal pools contain water for a few months in the spring and early summer.
This view of a pool shows a low water level in a dry spring. The greatest amount of biological activity in a pool takes place in the spring when the ice thaws. Vernal pool in summer. Vernal pools are often completely dry by summer or early fall, keeping them free of populations of fish. Some pools retain water year round yet have a low concentration of oxygen when warm and shallow, a condition which precludes fish.