All of the above are true, but the uses described have not been without conflict. Every one of these uses alters the natural ecological functioning of an estuary. If we are to preserve the estuarine functions we value, we need to understand how the system works, what constitutes an estuary, what its values and functions are, how our actions affect them, and how we should protect the features and the functions. It carries, besides the water itself, all of the substances dissolved in the water and all materials suspended in it. When this mixture meets seawater, the chemical properties of some of the river's contents change.
Fine sediments coagulate as the water becomes saltier.
These larger pieces then disperse, creating a turbid area in the upper estuary. Substances whose water solubility is low, such as fatty materials, including oils and many industrial chemicals, are absorbed by the particles and settle with them. These muds fill in river channels, make mud banks, and form the foundations for marshes. If the muds contain pollutants, they will be fixed in place where the mud settles. Estuarine sedimentation is a natural process that has many benefits, but also presents problems.