Levar Burton introduces this episode by discussing how essential it is to the environment. He joins the crew of marine biologists who examin e the condition of marine life with water and sea bottom samples. "Jac k, the Seal, and the Sea" by Gerald Aschenbreuner is read by Leslie Ug gams. Back on the marine biologist expedition, Burton learns technique s for determining the health of sea ecosystems. Among the specimins co llected are a leopard shark and a skate. Children describe ways to hel p protect the environment and suggest other books about water: "Water- -What it is. What it Does", A Day in the Life of a Marine Biologist", and "Sterling--The Rescue of a Baby Harbor Seal".