Final answer:
River activities affect coastal processes by building landforms through sediment deposits, impacting marine habitats through damming that alters sediment flow, and affecting water quality, which risks the health of marine organisms.
Step-by-step explanation:
The activities of a river can significantly affect coastal processes in a number of ways. For example, rivers with high silt content can create landforms such as deltas when they deposit sediments at the point where they enter the ocean or a lake, especially in areas where currents and waves are weak. In contrast, rivers with low silt content or those that empty into areas with strong ocean currents or wave action create estuarine areas where salt water and fresh water mix.
Furthermore, the construction of dams on rivers can have substantial impacts on coastal areas. Dams can restrict the flow of sediment downstream, which can starve beaches of sediment and lead to a narrowing of the coastal zone. This can affect the habitat of marine organisms and lead to alterations in the local ecology. Additionally, damming of rivers can alter flow regimes downstream, which may affect populations of fish and amphibians that require specific flow conditions for their lifecycle. It should be noted, however, that dams do not cause sea levels to drop, as the volume of water they trap is not large enough to have a global impact on sea levels.
Rivers also play a role in transporting sediment to beaches, which can fuel the construction of coastal landforms and contribute to the growth of the coastline. However, when rivers are poorly managed or polluted, it can result in poor water quality that damages the marine environment and affects the organisms living in it.