Runoff is the water that flows over the surface of the land and into nearby creeks, streams, and rivers when there is more water than the land can absorb. A runoff lake is a type of lake that forms when water from precipitation or melting snow flows over the surface of the land and collects in a low-lying area. Runoff lakes are typically shallow and can be found in areas with a lot of precipitation or in areas where the land is flat and low-lying.

Surface runoff is a major component of the water cycle and is the primary agent of soil erosion by water. It occurs when excess rainwater, stormwater, meltwater, or other sources can no longer sufficiently rapidly infiltrate the soil. This can occur when the soil is saturated by water to its full capacity, and the rain arrives more quickly than the soil can absorb it. Surface runoff often occurs because impervious areas such as roofs and pavement do not allow water to soak into the ground.

Urbanization has changed the dynamics of runoff by impacting the land itself. Infrastructure reduces the amount of permeable land into which water can absorb, causing more stormwater to pass over the surface, necessitating drainage systems to prevent flooding. The connection between wildfires and subsequent flooding has been attributed to the increased runoff that is unable to absorb into the scorched earth. Additionally, more pollutants like pesticides can be introduced as runoff flows over contaminated areas.

In summary, a runoff lake is a type of lake that forms when water from precipitation or melting snow flows over the surface of the land and collects in a low-lying area. Runoff is the water that flows over the surface of the land and into nearby creeks, streams, and rivers when there is more water than the land can absorb. Surface runoff is a major component of the water cycle and is the primary agent of soil erosion by water. Urbanization has changed the dynamics of runoff by impacting the land itself.