Adult Program Sponsored by the Needham Conservation Commission Join Joy Marzolf, Naturalist and Educator, for an adult evening program. What is a vernal pool? It is a fresh water pool that may only have water in winter, spring and early summer and may dry up by fall. In the spring vernal pool animals are often in a race against time for survival before the pool dries up. Learn about these seasonal pools and the many creatures that might inhabit them.