The bay is both geologically and hydrologically complex. The tide has an average range of (and range that can exceed 26 feet) and there are strong currents as large volumes of sea water flow into and out of the bay twice a day. The bay is very shallow with the average depth being about and about one third of its area is exposed at low water. The volume of freshwater entering from streams is relatively small and the nutrient rich waters support a great diversity of phytoplankton and algae. These support a biodiverse community of fish, shellfish, marine worms and other invertebrates. Many birds feed on these and the bay is an important visiting place for migrating birds and waterfowl.