Although virtually all Oregon estuaries have some marine component to them, Sand Lake estuary and Netarts Bay are two where the marine component dominates because they lack major freshwater inflow. The bay portion of the estuary is characterized by broad mud flats which are exposed to the air at low tide and flooded by a mix of salt and fresh waters at high tide. These flats are not just mud. Sand grains carried from the mountains by the river are deposited in the upper bay and along the edges of main channels, while finer particles of silt and clay drift farther to the edges of the flats near the fringing marshes. The catalyst for the tremendous productivity of the bay subsystem is the broad expanse of shallow, nutrient-rich water which covers these flats twice a day.
Solar energy drives the collective metabolism of the estuary.
The majority of the larger estuaries on the Oregon coast have extensive bay components. Alsea Bay, Yaquina Bay, Siletz Bay, and Coos Bay, for example, have relatively large bays as part of their estuarine system. Slough Sloughs are the smaller tributaries to the main bay and river channels. They have little freshwater inflow. Tidal flushing may not be as complete as in parts of the estuary that are closer to the ocean or main channel.