Why is there more water the nearer you get to the mouth?

As rivers approach their mouths, they typically accumulate more water due to the convergence of tributaries that feed into the main river. Additionally, sediment deposition and the widening of the river channel can create a larger volume of water in that area. Furthermore, the river may also receive input from groundwater and rainfall, contributing to increased water levels near the mouth. This accumulation is essential for maintaining ecosystems and supporting various forms of wildlife.