Final answer:
Rivers will not have deltas when they have low silt content or when they are in areas where ocean currents or wave action are high. In such cases, estuarine areas are created instead.
Step-by-step explanation:
Rivers will not have deltas when they have low silt content or when they are in areas where ocean currents or wave action are high. In such cases, the rivers will create estuarine areas where fresh water and salt water mix instead of building deltas.
For example, the Mississippi River delta in the Gulf of Mexico is formed because the river carries a lot of silt and the ocean currents and wave action are minimal. On the other hand, the Tigris and Euphrates rivers in Mesopotamia don't form deltas because they have low silt content and the currents and wave action are high.